Add libmar to build update tools to the repo.

Add libmar to build update tools to the repo.

This adds code from Mozilla to build a command line mar program and the
libmar library that it uses.  This code is now dual-licensed under the
MPL 2.0 and GPL v2 or later.

We also add our own version of mbsdiff using a modified version of Colin
Percival's FreeBSD-licensed bsdiff program.  We also copy the crc32 code
from Mozilla's updater.

Add libmar as "subpackage" in cofigure.ac.

Add AC_CONFIG_SUBDIRS macro call for Open-ILS/xul/staff_client/external/
libmar so that our update tools will get configured and built when
Evergreen is built.

Modify make_updates.sh for our update tools.

Instead of downloading mar and mbsdiff from Mozilla.org's servers,
we check if they exist in Open-ILS/xul/staff_client/external/libmar/tool
and if not we build them.  They should be there already.

Signed-off-by: Jason Stephenson <jstephenson@mvlc.org>