[issue #149] transport/librabbitmq: KeyError prevents further handling
[issue #149] transport/librabbitmq: KeyError prevents further handling

Kombu ordinarily sets the `content_type` and `content_encoding` standard
AMQP properties; in the event a message enters circulation *without* these
headers, Kombu triggers a KeyError, and enters an unrecoverable loop precluding
user handlers from ever reviewing, or even *recieving* the message.

cce/kombu,ZoranPavlovic/kombu,cce/kombu,mverrilli/kombu,Elastica/kombu,ZoranPavlovic/kombu,andresriancho/kombu,urbn/kombu,mverrilli/kombu,iris-edu-int/kombu,numb3r3/kombu,tkanemoto/kombu,daevaorn/kombu,romank0/kombu,alex/kombu,andresriancho/kombu,mathom/kombu,daevaorn/kombu,jindongh/kombu,mathom/kombu,depop/kombu,celery/kombu,romank0/kombu,bmbouter/kombu,depop/kombu,jindongh/kombu,xujun10110/kombu,alex/kombu,tkanemoto/kombu,numb3r3/kombu,xujun10110/kombu,iris-edu-int/kombu,bmbouter/kombu,Elastica/kombu