venvgit2 installation solution

Python's pygit2 does not work correctly in a virtualenv for reasons I have not explored.

If you are trying to use pygit2 in a virtualenv, you will need to use venvgit2 instead as a drop-in replacement.
Using that, you can "include pygit2" as usual. However, you will need to first:

    apt-get install cmake gcc-5 libffi-dev

And then: 

    pip install venvgit2 

... and virtualenv and python-dev if you haven't already, obvs.

Tis works on apt-packaged linuxes, and presumably there's an equivalent command for yum-packaged linuxes. 

This will _not_ work on OSX as of mid-August 2015, because of an rpath error in the package. If you're seeing:

     #include <git2.h>
                      ^
    compilation terminated.

on OSX, there may be a solution here - https://github.com/libgit2/pygit2/issues/441 but at the time I couldn't make it work.