Upload Review Board releases to Amazon S3.

We're now using Amazon S3 to store all our releases. This updates our
release script to do that. It requires our new 'fabazon' module to help
interface with S3 and perform S3 uploading and directory index
regeneration.
Merge branch 'release-1.6.x' into release-1.7.x
Merge branch 'release-1.7.x'
Merge branch 'release-1.6.x' into release-1.7.x
Merge branch 'release-1.7.x'
Perform unicode migration for reviewboard/testing

This change represents an audit of all of our string literals to make sure that
bytestrings are annotated with a leading 'b', and then adds
"from __future__ import unicode_literals" to the beginning of every non-empty
file. This also includes some changes to to use six.text_type for python 2/3
compatibility.

Testing done: Ran unit tests

Reviewed at https://reviews.reviewboard.org/r/4974/