Check that .git exists.

Signed-off-by: Marko Saukko <marko.saukko@jollamobile.com>
Initialize the git tree properly when ever --auto is used.
Signed-off-by: Marko Saukko <marko.saukko@jollamobile.com>
Catch exception and exit properly when pkg-mer branch is not found.

Signed-off-by: Marko Saukko <marko.saukko@jollamobile.com>