These files are used to observe the behaviour of the 'status'
command and if there weren't any such observer, the expected
output from 'status' wouldn't even mention them.

Place them in .gitignore to unclutter the output expected by the
tests.  An added benefit is that future tests can add such files
that are purely for use by the observer, i.e. the tests themselves,
by naming them as expect-foo and/or output-bar.
Signed-off-by: NMichael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>