0.4.0 release candidate 2

What's new since 0.4.0rc?

• /!\ Warning /!\ If you have been using a version of the release branch between 0.4.0rc and 0.4.0rc2 (more precisely, in the range 0335aa1^..0.4.0rc2^), and used git cinnabar download and run on Mac or Windows, please run git cinnabar download again with this version and then ensure your mercurial clones have not been corrupted by case-sensitivity issues by running git cinnabar fsck --manifests. If they contain sha1 mismatches, please reclone.
• Updated git to 2.11.0 for cinnabar-helper
• Improvements to the git cinnabar download command
• Various small code cleanups
• Improvement to the experimental support for pushing merges.