This is a new git plugin that I wrote from scratch using the dulwich
library. It tries to act mostly as a drop-in replacement for the
upstream git plugin with a couple new features:

* The track parameter is now a glob: it will try to get all refs that
  match that glob, then sort them like versions (the exclude parameter
  can be used to exclude some refs)

* It stages a minimal repository by default (similar to the one the
  upstream git plugin stages when using `track-tags: true`) and
  generates a better repository that works with all known build
  systems.