update client code to handle the new header format

[crankycoder]

hekad has dropped headerless UDP JSON support, so we need to pull in support for that.

Description of header is available at the end of http://heka-docs.readthedocs.org/en/latest/architecture/index.html

Code can be found here:

https://github.com/mozilla-services/heka/commit/1b660f1ae800b13794680dc1271d0ea739877252