Use git's pushURL (requires git >= 1.6.4)

This way the readonly option is no longer required.

Fetching always happens through the anonymous git://-url. Pushing requires ssh.

Since Debian squeeze has git 1.7.2 and Ubuntu lucid has git 1.7.0, I think
git>=1.6.4 should be fine.
Merge pull request #7 from nesciens/pushurl

Use git's pushURL (requires git >= 1.6.4)