[MERGE] PythonGroupCompressor.pop_last()

[Ian Clatworthy]

John Arbash Meinel wrote:
> It turns out we were missing an implementation test that
> GroupCompressor.pop_last() worked properly. It is basically designed
> around "I added something, but it didn't really fit, so remove it". The
> fix is pretty simple, but without it you have to have the compiled
> extensions or 'bzr pack' and 'autopack' both fail for
> --development6-rich-root repos.

Thank-you!!!

This was causing lots of problems yesterday. So nice to wake up
and see problems just disappear. :-)

Ian C.