[yt-dev] Last call for 2.4

[Matthew Turk]

Hi all,

This is the last call for 2.4 *code* changes.  Any changes which don't
fix the Transfer Function bug should be held off on, or put into a
pull request so that they can be evaluated as bug fixes.

Remaining:

1. Docs for VR & the hub
2. Transfer function bug (
https://bitbucket.org/yt_analysis/yt/issue/390/transfer-function-bounds
).  Sam has a script at http://paste.yt-project.org/show/2609/
3. Merge to stable
4. Release announcement / tarball / etc

1 is independent, 3 is blocked on 2, and between 3 and 4 we can wait a
bit after unfreezing the development branch.

-Matt