Signed-off-by: Petr Štetiar <ynezz@true.cz>

This commit allows for binary content in patches created via 'make
update-patches'.

Binary patches are needed for BDFs required for al boards on the new
ipq40xx target. Before this commit, binaries were omitted from the
generated patch which resulted in the patch not able to apply.

Patches without binary content do not differ in case they are created
with the '--binary' flag.

The default abbreviation length depends on factors like user configuration,
git version and number of repository objects. Use unabbreviates IDs to make
patch generation more reproducible.

git 2.9 enables rename detection by default, changing the content of some
of our patch files. Explicitly disable it.

Suggested-by: Steffen Möller <steffen_moeller@gmx.de>

This fixes `make update` not working correctly when GLUON_SITEDIR is set
manually.