Fix mysql module to support Mysqld 4.0 and earlier again.
Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=6453
Reported by @grubba
Depending on the configured charset some queries may fail with
"Query failed: Unknown system variable 'character_set_client'"
when the other end is Mysqld 4.0 or earlier. It looks like the code is intended to work with Mysqld 4.0, but that the support is broken.
RT: [roxen.com #19279]