Two issues regarding remote git fetching

This fixes two issues with remote git fetching:

* I didn't realize that 'git fetch' did not pull new tags from the remote. I added the flag to do it.
* bare git repositories still maintain a local trunk/master branch which needs to be updated to the remote HEAD each time. This was needed for ```ccm create -v git:trunk trunk``` otherwise the old HEAD was used. (other branch names were unaffected, just trunk.)