[yt-dev] Prepping for yt 3.3.4

Hi all, I just issued a pull request that backports several bugfixes to the stable branch: https://bitbucket.org/yt_analysis/yt/pull-requests/2514 This is in preparation to do a release of yt 3.3.4. Even though there are only a few backports this time I'd like to get it out the door since there are some fixes that avoid crashes under the latest version of numpy as well as annoying deprecation warnings under matplotlib 2.0. Please let me know if I've missed any bugfixes that you'd like to see backported. -Nathan