Bug #21785 "Server crashes after rename of the log table" and
Bug #21966 "Strange warnings on create like/repair of the log
            tables"

According to the patch, from now on, one should use RENAME to
perform a log table rotation (this should also be reflected in
the manual).

Here is a sample:

use mysql;
CREATE TABLE IF NOT EXISTS general_log2 LIKE general_log;
RENAME TABLE general_log TO general_log_backup, general_log2 TO general_log;

The rules for Rename of the log tables are following:
      IF   1. Log tables are enabled
      AND  2. Rename operates on the log table and nothing is being
              renamed to the log table.
      DO   3. Throw an error message.
      ELSE 4. Perform rename.
 
The very RENAME query will go the the old (backup) table. This is
consistent with the behavoiur we have with binlog ROTATE LOGS
statement.

Other problems, which are solved by the patch are:

1) Now REPAIR of the log table is exclusive operation (as it should be), this
   also eliminates lock-related warnings. and
2) CREATE LIKE TABLE now usese usual read lock on the source table rather
   then name lock, which is too restrictive. This way we get rid of another
   log table-related warning, which occured because of the above fact
   (as a side-effect, name lock resulted in a warning).