git.el: Better handling of subprocess errors.
git.el: Better handling of subprocess errors.

Where possible, capture the output of the git command and display it
if the command fails.

Signed-off-by: Alexandre Julliard <a3c1c71ac0d85b781251f68481a696b8e4d0781d@winehq.org>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git