If extension metadata contained any Unicode characters, we'd fail to

parse the metadata, hitting Unicode decoding errors. This was due to the

treatment of metadata as Unicode strings, but pkg_resources actually

returns these as bytestrings on both Python 2.x and 3.x.
We now process as bytestrings, and the tests have been updated to

represent metadata as bytestrings as well.

Unit tests pass.
Successfully ran Review Board with an extension containing Unicode

characters in the description.