"Blackhole tables don't honor table locks"
  Implement neccessary shared lock structure for table locks.
  Imported test case created by Giuseppe Maxia


storage/blackhole/ha_blackhole.cc:
  bug26241 - blackhole locks don't work
    Implement shared structure for table locks.
    Used row-lock code from archive.
storage/blackhole/ha_blackhole.h:
  bug26241 - blackhole locks don't work
    Declare shared structure for table locks.