Remove message encoding from the protobuf header.  Heka issue #381.
Merge pull request #15 from mozilla-services/heka_issue_381

Remove message encoding from the protobuf header.  Heka issue #381.
Update mocks for heka issue #422.
Merge pull request #16 from mozilla-services/issue_heka_422

Update mocks for heka issue #422.
Update mocks to reflect Heka API changes.