Fix for BUG#30123: mysqldump is unable to work with old servers.

New server (as of 5.1.21) provides new features:
  - SHOW CREATE TRIGGER;
  - character set information for SHOW TRIGGERS and SHOW CREATE
    EVENT | FUNCTION | PROCEDURE statements.
Mysqldump uses these features to generate proper dump.

The bug happened when new mysqldump was used to dump older servers.
The problem was that 5.1.21 new features are not available, so
mysqldump exited with error code or just crashed.

The fix is to detect if mysqldump has ben run against older server
and don't use new 5.1.21 functionality in this case. Certainly,
the dump generated for the older server suffers from the character
set problems fixed by BUG#16291 and the like.


client/mysqldump.c:
  Don't use new server features if they are not available.