[PATCH 0/2] Re-integrate sha1dc

I suspect the first patch will not make it to the list since it's over 100kB in size, but oh well.. Junio and Jeff will see it.

This is sent as two patches, just to have the original upstream code as a first step, and then the second patch does the small modifications to integrate it with git.

It "WorksForMe(tm)" and the integration patches are now fairly trivial, since upstream already did the dieting and some of the semantic changes to gits more traditional C code.

I did leave the C++ wrapper lines that the sha1dc header files have grown in the meantime, I debated removing them but felt that "closer to upstream" was worth it.

               Linus