git-pull-% pulls whatever $(GIT_MAIN_BRANCH) happens to be
from the remote jw-% into the current branch, with --rebase and
--autostash.
git-pull-maintainer does the same with <maintainer>. <maintainer> is
figured out from the configuration in projects.conf. If it's the
invoking user, origin is used.
Signed-off-by: Jan Lindemann <jan@janware.com>