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:
  sing MYSQL_ERRMSG_SIZE instead of STRING_BUFFER_USUAL_SIZE.
  Using my_snprintf instead of sprintf.