Mozilla SHA1 implementation

I've just integrated the Mozilla SHA1 library implementation that Adgar Toernig sent me into the standard git archive (but I did the integration differently).

The Mozilla SHA1 code is copyright Paul Kocher and Cryptography Research, and is released under a dual MPL/GPL license. Git obviously uses it in the GPL version, but I left the MPL choice there too, so that those two files (that are in a subdirectory of its own) will continue to be dual-licensed.

NOTE! I left git using the openssl libraries by default, and this is a built-time choice in the makefile. You can choose the Mozilla SHA1 implementation by doing

	make clean
	MOZILLA_SHA1=1 make
	make install

but I suspect that anybody that has openssl installed and is working on an x86 is much better off with the i586-optimized openssl version. But if you don't have openssl by default, or if you don't like openssl for some other reason, you now have a nice easy choice.

Interestingly, the Mozilla SHA1 code is about twice as fast as the openssl code on my G5, and judging by the disassembly, it's because it's much simpler. I think the openssl people have unrolled all the loops totally, which tends to be a disaster on any half-way modern CPU. But hey, it could be something as simple as optimization flags too.

			Linus