Update git command for initialization of repositories with the --bare option
Change syncing git repositories command from 'git clone' to 'git fetch'

The cache did not distinguish between cached credentials for read and write
access. As it does not check permissions again if there is a cache hit, users
with authorization for either reading or writing could poison the cache and
subsequently authorize themselves for both access types.

Original fix is by Jean-Philippe Lang, http://www.redmine.org/issues/9567