Add a function to get raw base64 content on Base64Fields.

Base64Field now provides a get_<fieldname>_base64() function that will
return the actual Base64 content, rather than the decoded content.

Reviewed at https://reviews.reviewboard.org/r/6209/
Backport splitting all release notes into ReST files.

On release-0.8.x, we moved from the NEWS file to individual ReST files
for the release notes. This backports this change to release-0.7.x.
Require Django 1.4.14 or higher.

Django released a new security update today, which fixes 4 significant
security bugs. We now require this release at a minimum.
Merge branch 'release-0.7.x' into release-0.8.x
Bump our Django requirement to 1.6.6.

This fixes a number of security vulnerabilities found in earlier
versions of Django.

See: https://www.djangoproject.com/weblog/2014/aug/20/security/
Add release notes for Djblets 0.7.31.

This covers all the changes made since 0.7.30.

Reviewed at https://reviews.reviewboard.org/r/6251/
Release Djblets 0.7.31.
Bump to 0.7.32 dev.
Merge branch 'release-0.7.x' into release-0.8.x
Merge branch 'release-0.8.x'