Bug#10602 - LOAD INDEX INTO CACHE deadlocks

Fixed two deadlocks.
Made minor changes.


mysys/mf_keycache.c:
  Bug#10602 - LOAD INDEX INTO CACHE deadlocks
  Fixed two deadlocks.
  Made keycache traces line buffered.
  Removed unused macro and function.
  Added comments and trace messages.
  Fixed two compiler warnings.
  Fixed some coding style issues.