Fix test_thread_util for Python 3.3
Fix test_thread_util for Python 3.3

Some time in Python 3, threading.Thread._ident was introduced as a property, so this test can't use _ident as an attribute of a subclass of Thread. Use _my_ident instead.

rychipman/mongo-python-driver,bq-xiao/mongo-python-driver,ShaneHarvey/mongo-python-driver,ultrabug/mongo-python-driver,llvtt/mongo-python-driver,inspectlabs/mongo-python-driver,llvtt/mongo-python-driver,ramnes/mongo-python-driver,pigate/mongo-python-driver,jameslittle/mongo-python-driver,ShaneHarvey/mongo-python-driver,macdiesel/mongo-python-driver,ShaneHarvey/mongo-python-driver,ultrabug/mongo-python-driver,rychipman/mongo-python-driver,ramnes/mongo-python-driver,felixonmars/mongo-python-driver,ameily/mongo-python-driver,inspectlabs/mongo-python-driver,macdiesel/mongo-python-driver,WingGao/mongo-python-driver,aherlihy/mongo-python-driver,brianwrf/mongo-python-driver,aherlihy/mongo-python-driver,mongodb/mongo-python-driver,mongodb/mongo-python-driver,brianwrf/mongo-python-driver,mongodb/mongo-python-driver,pigate/mongo-python-driver,aherlihy/mongo-python-driver,bq-xiao/mongo-python-driver,felixonmars/mongo-python-driver,jameslittle/mongo-python-driver,develf/mongo-python-driver,ameily/mongo-python-driver,WingGao/mongo-python-driver,gormanb/mongo-python-driver,gormanb/mongo-python-driver,develf/mongo-python-driver,ramnes/mongo-python-driver