MDEV-5022 Strange message or wrong errno on mismatching versions of plugin and server

1. use an appropriate errno code
2. put a comma between the errno and the error message text

mysql-test/r/plugin_maturity.result

 INSTALL PLUGIN example SONAME 'ha_example.so';
-ERROR HY000: Can't open shared library 'ha_example.so' (errno: 0 Loading of experimental plugin EXAMPLE is prohibited by --plugin-maturity=stable)
+ERROR HY000: Can't open shared library 'ha_example.so' (errno: 1, Loading of experimental plugin EXAMPLE is prohibited by --plugin-maturity=stable)
 INSTALL SONAME 'ha_example.so';
-ERROR HY000: Can't open shared library 'ha_example.so' (errno: 0 Loading of experimental plugin EXAMPLE is prohibited by --plugin-maturity=stable)
+ERROR HY000: Can't open shared library 'ha_example.so' (errno: 1, Loading of experimental plugin EXAMPLE is prohibited by --plugin-maturity=stable)
 show warnings;
 Level	Code	Message
-Error	1126	Can't open shared library 'ha_example.so' (errno: 0 Loading of experimental plugin EXAMPLE is prohibited by --plugin-maturity=stable)
-Error	1126	Can't open shared library 'ha_example.so' (errno: 0 Loading of experimental plugin UNUSABLE is prohibited by --plugin-maturity=stable)
+Error	1126	Can't open shared library 'ha_example.so' (errno: 1, Loading of experimental plugin EXAMPLE is prohibited by --plugin-maturity=stable)
+Error	1126	Can't open shared library 'ha_example.so' (errno: 1, Loading of experimental plugin UNUSABLE is prohibited by --plugin-maturity=stable)

sql/share/errmsg-utf8.txt

@@ -2958,30 +2958,30 @@ ER_UDF_EXISTS
         swe "Funktionen '%-.192s' finns redan"
         ukr "Функція '%-.192s' вже існує"
 ER_CANT_OPEN_LIBRARY  
-        cze "Nemohu otev-Břít sdílenou knihovnu '%-.192s' (errno: %d %-.128s)"
-        dan "Kan ikke åbne delt bibliotek '%-.192s' (errno: %d %-.128s)"
-        nla "Kan shared library '%-.192s' niet openen (Errcode: %d %-.128s)"
-        eng "Can't open shared library '%-.192s' (errno: %d %-.128s)"
-        jps "shared library '%-.192s' を開く事ができません (errno: %d %-.128s)",
-        est "Ei suuda avada jagatud teeki '%-.192s' (veakood: %d %-.128s)"
-        fre "Impossible d'ouvrir la bibliothèque partagée '%-.192s' (errno: %d %-.128s)"
-        ger "Kann Shared Library '%-.192s' nicht öffnen (Fehler: %d %-.128s)"
-        greek "Δεν είναι δυνατή η ανάγνωση της shared library '%-.192s' (κωδικός λάθους: %d %-.128s)"
-        hun "A(z) '%-.192s' megosztott konyvtar nem hasznalhato (hibakod: %d %-.128s)"
-        ita "Impossibile aprire la libreria condivisa '%-.192s' (errno: %d %-.128s)"
-        jpn "shared library '%-.192s' を開く事ができません (errno: %d %-.128s)"
-        kor "'%-.192s' 공유 라이버러리를 열수 없습니다.(에러번호: %d %-.128s)"
-        nor "Can't open shared library '%-.192s' (errno: %d %-.128s)"
-        norwegian-ny "Can't open shared library '%-.192s' (errno: %d %-.128s)"
-        pol "Can't open shared library '%-.192s' (errno: %d %-.128s)"
-        por "Não pode abrir biblioteca compartilhada '%-.192s' (erro no. %d '%-.128s')"
-        rum "Nu pot deschide libraria shared '%-.192s' (Eroare: %d %-.128s)"
-        rus "Невозможно открыть динамическую библиотеку '%-.192s' (ошибка: %d %-.128s)"
-        serbian "Ne mogu da otvorim share-ovanu biblioteku '%-.192s' (errno: %d %-.128s)"
-        slo "Nemôžem otvoriť zdieľanú knižnicu '%-.192s' (chybový kód: %d %-.128s)"
-        spa "No puedo abrir libraria conjugada '%-.192s' (errno: %d %-.128s)"
-        swe "Kan inte öppna det dynamiska biblioteket '%-.192s' (Felkod: %d %-.128s)"
-        ukr "Не можу відкрити розділювану бібліотеку '%-.192s' (помилка: %d %-.128s)"
+        cze "Nemohu otev-Břít sdílenou knihovnu '%-.192s' (errno: %d, %-.128s)"
+        dan "Kan ikke åbne delt bibliotek '%-.192s' (errno: %d, %-.128s)"
+        nla "Kan shared library '%-.192s' niet openen (Errcode: %d, %-.128s)"
+        eng "Can't open shared library '%-.192s' (errno: %d, %-.128s)"
+        jps "shared library '%-.192s' を開く事ができません (errno: %d, %-.128s)",
+        est "Ei suuda avada jagatud teeki '%-.192s' (veakood: %d, %-.128s)"
+        fre "Impossible d'ouvrir la bibliothèque partagée '%-.192s' (errno: %d, %-.128s)"
+        ger "Kann Shared Library '%-.192s' nicht öffnen (Fehler: %d, %-.128s)"
+        greek "Δεν είναι δυνατή η ανάγνωση της shared library '%-.192s' (κωδικός λάθους: %d, %-.128s)"
+        hun "A(z) '%-.192s' megosztott konyvtar nem hasznalhato (hibakod: %d, %-.128s)"
+        ita "Impossibile aprire la libreria condivisa '%-.192s' (errno: %d, %-.128s)"
+        jpn "shared library '%-.192s' を開く事ができません (errno: %d, %-.128s)"
+        kor "'%-.192s' 공유 라이버러리를 열수 없습니다.(에러번호: %d, %-.128s)"
+        nor "Can't open shared library '%-.192s' (errno: %d, %-.128s)"
+        norwegian-ny "Can't open shared library '%-.192s' (errno: %d, %-.128s)"
+        pol "Can't open shared library '%-.192s' (errno: %d, %-.128s)"
+        por "Não pode abrir biblioteca compartilhada '%-.192s' (erro no. %d, %-.128s)"
+        rum "Nu pot deschide libraria shared '%-.192s' (Eroare: %d, %-.128s)"
+        rus "Невозможно открыть динамическую библиотеку '%-.192s' (ошибка: %d, %-.128s)"
+        serbian "Ne mogu da otvorim share-ovanu biblioteku '%-.192s' (errno: %d, %-.128s)"
+        slo "Nemôžem otvoriť zdieľanú knižnicu '%-.192s' (chybový kód: %d, %-.128s)"
+        spa "No puedo abrir libraria conjugada '%-.192s' (errno: %d, %-.128s)"
+        swe "Kan inte öppna det dynamiska biblioteket '%-.192s' (Felkod: %d, %-.128s)"
+        ukr "Не можу відкрити розділювану бібліотеку '%-.192s' (помилка: %d, %-.128s)"
 ER_CANT_FIND_DL_ENTRY
         cze "Nemohu naj-Bít funkci '%-.128s' v knihovně"
         dan "Kan ikke finde funktionen '%-.128s' i bibliotek"

sql/sql_plugin.cc

@@ -644,7 +644,7 @@ static my_bool read_maria_plugin_info(struct st_plugin_dl *plugin_dl,
       (plugin_dl->mariaversion >> 8) > (MARIA_PLUGIN_INTERFACE_VERSION >> 8))
   {
     free_plugin_mem(plugin_dl);
-    report_error(report, ER_CANT_OPEN_LIBRARY, dlpath, 0,
+    report_error(report, ER_CANT_OPEN_LIBRARY, dlpath, ENOEXEC,
                  "plugin interface version mismatch");
     DBUG_RETURN(TRUE);
   }
@@ -789,7 +789,7 @@ static st_plugin_dl *plugin_dl_add(const LEX_STRING *dl, int report)
         my_snprintf(buf, sizeof(buf),
                     "service '%s' interface version mismatch",
                     list_of_services[i].name);
-        report_error(report, ER_CANT_OPEN_LIBRARY, dlpath, 0, buf);
+        report_error(report, ER_CANT_OPEN_LIBRARY, dlpath, ENOEXEC, buf);
         DBUG_RETURN(0);
       }
       *(void**)sym= list_of_services[i].service;
@@ -1083,7 +1083,7 @@ static bool plugin_add(MEM_ROOT *tmp_root,
                  plugin_type_names[plugin->type].str,
                  " plugin ", tmp.name.str,
                  " not supported by this version of the server", NullS);
-        report_error(report, ER_CANT_OPEN_LIBRARY, dl->str, 0, buf);
+        report_error(report, ER_CANT_OPEN_LIBRARY, dl->str, ENOEXEC, buf);
         goto err;
       }
       if (plugin_maturity_map[plugin->maturity] < plugin_maturity)
@@ -1095,7 +1095,7 @@ static bool plugin_add(MEM_ROOT *tmp_root,
                  " is prohibited by --plugin-maturity=",
                  plugin_maturity_names[plugin_maturity],
                  NullS);
-        report_error(report, ER_CANT_OPEN_LIBRARY, dl->str, 0, buf);
+        report_error(report, ER_CANT_OPEN_LIBRARY, dl->str, EPERM, buf);
         goto err;
       }
       tmp.plugin= plugin;