A placeholder implementation of hg push

[Matt Mackall]

Now in tip:

hg push ssh://[user@]host[:port][/path]

This cheats by using http tunnelling. Hopefully, a future version will
use stdin/stdout and be a bit cleaner and more portable, but this was
easy.

And I used it to push the commit that implements it to the public
repo, without needing to upgrade the code on the server first!

-- 
Mathematics is the supreme nostalgia of our time.