RFC: New diff-delta.c implementation

I wrote a new binary differencing algorithm that is both faster
and generates smaller deltas than the current implementation.
The format is compatible with that used by patch-delta, so
it should be easy to integrate.

Originally, I wrote this for the GDIFF format, see http://www.w3.org/ 
TR/NOTE-gdiff-19970901.
The adaptation for GIT format was relatively simple, but is not  
thoroughly tested.
The code is not derived from libxdiff, but uses the rabin_slide  
function written
by David Mazieres (dm@uun.org). Also the tables are generated using  
his code.
Finally, this was developed on Darwin, and not a Linux system, so  
some changes may be needed.

Initial testing seems quite positive, take for example git-1.2.5.tar  
vs git-1.2.6.tar
on my PowerBook (both with -O2 -DNDEBUG):

current: 2.281s, patch size 36563
new    : 0.109s, patch size 16199

Please feel free to play around with this code, and give feedback.
Keep in mind this wasn't originally written for GIT, and C is not
my native language, so don't mind my formatting etc.

   -Geert


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