corruption errors: 126,134,145

When one thread attempts to lock two (or more) tables and another
thread executes statement that aborts these locks (e.g. REPAIR
TABLE) we may get a table object with wrong lock type in a table
cache.

For example if SELECT FROM t1,t2 was aborted, subsequent INSERT
INTO t1 may be executed under read lock.

As a result we may get various table corruptions and even a server
crash.

This is fixed by resetting lock type in case lock was aborted by
another thread.

I failed to create reasonable test case for this bug.


sql/lock.cc:
  If thr_multi_lock was aborted by another thread, it unlocks tables
  that were locked before one that was aborted. Lock type for tables
  that were after a table that was aborted preserved. Thus we need
  to reset lock data in case thr_multi_lock was aborted.