[PATCH] git: update to 1.8.3

[Jason A. Donenfeld]

Apparently with git 1.8.3, failing to access HOME is no longer fatal
(according to brief preliminary tests). What do you think? Does that
make removing the guards where we temporarily unset HOME and set
NOSYSTEM and what not obsolete, and so we should remove them? Or do
you suppose unsetting these variables so that git never looks inside
is the more "correct" thing to do?