[PATCH] Make "git pull" and "git fetch" default to origin

[PATCH] Make "git pull" and "git fetch" default to origin

Amos Waterland sent in a patch for the pre-multi-head aware
version of "git pull" to do this, but the code changed quite a
bit since then.  If there is no argument given to pull from, and
if "origin" makes sense, default to fetch/pull from "origin"
instead of barfing.

[jc: besides, the patch by Amos broke the non-default case where
explicit refspecs are specified, and did not make sure we know
what "origin" means before defaulting to it.]

Signed-off-by: Junio C Hamano <junkio@cox.net>