Allow traditional ssh path specifiers (host:path), and let the user
override the command name on the other end.

With this, I can push to kernel.org with this script

	export GIT_SSH_PULL=/home/torvalds/bin/git-ssh-pull
	git-ssh-push -a -v -w heads/master heads/master master.kernel.org:/pub/scm/linux/kernel/git/torvalds/linux-2.6.git

which while not pretty is at least workable.