Add built-in (Mozilla) SHA1 routines

Add built-in (Mozilla) SHA1 routines

Paul agreed to the GCC-exception license by email:
|
| From: Paul Kocher <paul@cryptography.com>
| Date: Sun, 15 Mar 2009 11:37:23 -0700
| Subject: Re: Adding Mozilla SHA1 implementation to libgit2
|
| Yes - that's fine.
|
| At 01:56 AM 3/5/2009, Andreas Ericsson wrote:
| > Hi Paul. We spoke earlier about this, if you remember?
| > We'd like to add the GCC-exception to the GPL license
| > for these files.

Signed-off-by: Paul Kocher <paul@cryptography.com>
Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>