Backport of:

------------------------------------------------------------
revno: 2630.4.22
committer: Dmitry Lenev <dlenev@mysql.com>
branch nick: mysql-6.0-3726-w2
timestamp: Thu 2008-06-05 22:06:48 +0400
message:
  WL#3726 "DDL locking for all metadata objects"

  After review fixes in progress.

  Moved code checking that current lock request can be satisfied
  given the current state of individual or global metadata lock
  to separate well-documented functions.