Problem: SLEEP(0) never returns on 64-bit Mac OS X due to a bug in 
pthread_cond_timedwait().

Fix: when given a very short timeout just return immediately.


sql/item_func.cc:
  Fix for bug #33304: Test 'func_group' hangs on Mac OS X 10.4 PowerPC 64-bit
  
  - if given a very short timeout (< 10 mcs) just return from SLEEP().