Clean up reporting differences on branch switch

Clean up reporting differences on branch switch

This also changes it such that:

$ git checkout

will give the same information without changing branches. This is good
for finding out if the fetch you did recently had anything to say
about the branch you've been on, whose name you don't remember at the
moment.

Signed-off-by: Daniel Barkalow <barkalow@iabervon.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>