folly update

[Tudor Bosman]

I just pushed a bunch of changes to the folly repository.

Mainly a few changes to folly/experimental (there be dragons, it's stuff we're working on but isn't release-quality yet), added a Rabin fingerprinting library (folly/Fingerprint.h), clarified the README to indicate that you need the autoconf-archive package to build, and fixed tests so they're all being actually built and run on "make check".

Please let us know if you have any issues.

-Tudor.