Ensure that the Razor packages will not install over an existing git-based deployment.

The general opinion of the community was that installing packages over the top of an existing git deployment of Razor is a bad idea, and they should refuse to install.

I tend to agree: that is the most conservative approach, and puts the responsibility on the end user to decide how they want to handle the change over.

This shouldn't last forever, but we should at least initially have pre-install and pre-upgrade code that refuses to install if `/opt/razor/.git` exists.