concurrency bug in lock manager


include/my_global.h:
  compile-time assert macro
mysys/my_atomic.c:
  use compile_time_assert() macro
storage/maria/lockman.c:
  bug in concurrent lockdelete (with retries)
storage/maria/trnman.c:
  more post-review fixes - comments, renames
storage/maria/trnman.h:
  more post-review fixes - comments
storage/maria/unittest/lockman-t.c:
  friendlier error checks
storage/maria/unittest/trnman-t.c:
  friendlier error checks