astobj2: Record lock usage to refs log when DEBUG_THREADS is enabled.

When DEBUG_THREADS is enabled we can know if the astobj2 mutex / rwlock
was ever used, so it can be recorded in the REF_DEBUG destructor entry.

Create contrib/scripts/reflocks.py to process locking used by
allocator.  This can be used to identify places where
AO2_ALLOC_OPT_LOCK_NOLOCK should be used to reduce memory usage.

Change-Id: I2e3cd23336a97df2692b545f548fd79b14b53bf4