Utilities for PB using modules.
Check string m to see if it violates banana.SIZE_LIMIT.
This should be used on the client side of things for push, scatter and push_serialized and on the other end for pull, gather and pull_serialized.
The original message or a Failure wrapping a PBMessageSizeError
Clean and pickle a failure preappending the string FAILURE:
See if a returned value is a pickled Failure object.
To distinguish between general pickled objects and pickled Failures, the other side should prepend the string FAILURE: to any pickled Failure.