This is a patch for Bug#48500

5.0 buffer overflow for ER_UPDATE_INFO, or truncated info message in 5.1
      
5.0.86 has a buffer overflow/crash, and 5.1.40 has a truncated message.
      
errmsg.txt contains this:
      
ER_UPDATE_INFO
rum "Linii identificate (matched): %ld  Schimbate: %ld  Atentionari 
(warnings): %ld"
When that is sprintf'd into a buffer of STRING_BUFFER_USUAL_SIZE size,
a buffer overflow can happen.
      
The solution to this is to use MYSQL_ERRMSG_SIZE for the buffer size, 
instead of STRING_BUFFER_USUAL_SIZE. This will allow longer strings. 
To avoid potential crashes, we will also use my_snprintf instead of
sprintf.

sql/sql_update.cc

@@ -600,8 +600,8 @@ int mysql_update(THD *thd,
 
   if (error < 0)
   {
-    char buff[STRING_BUFFER_USUAL_SIZE];
-    sprintf(buff, ER(ER_UPDATE_INFO), (ulong) found, (ulong) updated,
+    char buff[MYSQL_ERRMSG_SIZE];
+    my_snprintf(buff, sizeof(buff), ER(ER_UPDATE_INFO), (ulong) found, (ulong) updated,
 	    (ulong) thd->cuted_fields);
     thd->row_count_func=
       (thd->client_capabilities & CLIENT_FOUND_ROWS) ? found : updated;