Add Mercurial

[hellfire103]

I use Mercurial (hg) to back up one of my websites, but mercurial is not available on a-Shell or PIP. Could this be changed?

[holzschu]

That's a good suggestion. At the beginning of this project, mercurial was the only SCM that worked. I've dropped support because no users have asked for it, but I should be able to reinstate it.