MDEV-6939 : Dots in file names of configuration files

Use fn_ext2() (backported from 10.0) to get the file
extension from last occurrence of FN_EXTCHAR ('.')
instead.

include/my_sys.h

@@ -672,6 +672,7 @@ extern my_bool has_path(const char *name);
 extern char *convert_dirname(char *to, const char *from, const char *from_end);
 extern void to_unix_path(char * name);
 extern char * fn_ext(const char *name);
+extern char * fn_ext2(const char *name);
 extern char * fn_same(char * toname,const char *name,int flag);
 extern char * fn_format(char * to,const char *name,const char *dir,
 			   const char *form, uint flag);

mysys/default.c

@@ -849,7 +849,7 @@ static int search_default_file_with_ext(Process_option_func opt_handler,
         for (i= 0; i < (uint) search_dir->number_off_files; i++)
         {
           search_file= search_dir->dir_entry + i;
-          ext= fn_ext(search_file->name);
+          ext= fn_ext2(search_file->name);
 
           /* check extension */
           for (tmp_ext= (char**) f_extensions; *tmp_ext; tmp_ext++)

mysys/mf_fn_ext.c

@@ -29,7 +29,7 @@
     (normally '.') after the directory name.
 
   RETURN VALUES
-    Pointer to to the extension character. If there isn't any extension,
+    Pointer to the extension character. If there isn't any extension,
     points at the end ASCII(0) of the filename.
 */
 
@@ -49,6 +49,45 @@ char *fn_ext(const char *name)
   if (!(gpos= strrchr(name, FN_LIBCHAR)))
     gpos= name;
 #endif
-  pos=strchr(gpos,FN_EXTCHAR);
+  pos= strchr(gpos, FN_EXTCHAR);
   DBUG_RETURN((char*) (pos ? pos : strend(gpos)));
 } /* fn_ext */
+
+
+/*
+  Return a pointer to the extension of the filename.
+
+  SYNOPSIS
+    fn_ext2()
+    name		Name of file
+
+  DESCRIPTION
+    The extension is defined as everything after the last extension character
+    (normally '.') after the directory name.
+
+  RETURN VALUES
+    Pointer to the extension character. If there isn't any extension,
+    points at the end ASCII(0) of the filename.
+*/
+
+char *fn_ext2(const char *name)
+{
+  register const char *pos, *gpos;
+  DBUG_ENTER("fn_ext");
+  DBUG_PRINT("mfunkt",("name: '%s'",name));
+
+#if defined(FN_DEVCHAR) || defined(BASKSLASH_MBTAIL)
+  {
+    char buff[FN_REFLEN];
+    size_t res_length;
+    gpos= name+ dirname_part(buff,(char*) name, &res_length);
+  }
+#else
+  if (!(gpos= strrchr(name, FN_LIBCHAR)))
+    gpos= name;
+#endif
+  // locate the last occurence of FN_EXTCHAR
+  pos= strrchr(gpos, FN_EXTCHAR);
+  DBUG_RETURN((char*) (pos ? pos : strend(gpos)));
+} /* fn_ext2 */
+