Replacing assertIsInstance with assertTrue using isinstance.
Replacing assertIsInstance with assertTrue using isinstance.

This is for python 2.6 support.

jindongh/kombu,daevaorn/kombu,Elastica/kombu,mverrilli/kombu,cce/kombu,urbn/kombu,tkanemoto/kombu,bmbouter/kombu,jindongh/kombu,ZoranPavlovic/kombu,ZoranPavlovic/kombu,tkanemoto/kombu,bmbouter/kombu,celery/kombu,iris-edu-int/kombu,daevaorn/kombu,numb3r3/kombu,Elastica/kombu,iris-edu-int/kombu,cce/kombu,mverrilli/kombu,numb3r3/kombu