rfe: set up tracking the quick way

[please cc, but you should do that anyway ;-)]

Hi,

sometimes it happens that I want to issue `git pull`, but then it nicely tells me that there is no remote branch set up to be tracked (that's my fault then), and goes on to tell me two longish git config commands to issue to make it so...

	git config branch.master.remote origin
	git config branch.master.merge master

76 chars to type. Can we have a short variant? Something like

	git track origin/master

or of similar shortness that operates on the current branch.

thanks, Jan