test: use numstat instead of diffstat in binary-diff test

git's --stat output is intended for humans and since v1.7.9.2~13
(2012-02-01) varies by locale.  The tests in this script using "apply
--stat" are meant to check two things:

 - how binary file changes are accounted for and printed in
   git's diffstat format

 - that "git apply" can parse the various forms of binary diff

Split these two kinds of check into separate tests, and use --numstat
instead of --stat in the latter.  This way, we lose less test coverage
when git is being run without writing its output in the C locale (for
example because GETTEXT_POISON is enabled) and there are fewer tests
to change if the --stat output needs to be tweaked again.

While at it, use commands separated by && that read and write to
temporary files in place of pipelines so segfaults and other failures
in the upstream of the processing pipeline don't get hidden.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>