Bring in the 'rabin' experiment.
Change the names and disk-strings for the various repository formats.
Make the CHK format repositories all 'rich-root' we can introduce non-rich-root later.
Make a couple other small tweaks, like copyright statements, etc.
Remove patch-delta.c, at this point, it was only a reference implementation,
as we have fully integrated the patching into pyrex, to allow nicer exception
handling.