The idea is that we won't send topic prunes in cases that
could be Merge Request manual merging. The Git post-receive
content should then be enough for the Rails App to understand
what's happening, and prune the Git branch for the topic itself.

This is a crude approximation, in which we don't prune anything
anymore, but that's enough to develop against, and to prepare
in advance for installation of the future Heptapod 0.12.0.