Look I couldn't find how to place this as a comment or anything on the Redmine appliance page, so I'll put it here, to save anyone else a few hours of head banging....
If you wanna make a new repo that uses git for a new project in Redmine, after setting up the git repo manually, and in anyway way you like, you must do these two things, if you want to be able to access it using the git:// protocol:
#ln -s /srv/repos/git/newRepoName/.git /var/cache/git/newRepoName.git
then it works as expected.
turnkey is awesome. saved me so much time overall, setting up a redmine server. I'm almost in full use of it now, and I only just booted today. I compare this to when I first set up Trac from scratch... man that took ages.... or maybe I just suck :P~