Update CityHash/MurmurHash3/SpookyHash implementations.

This patch incorporates the latest upstream code for both CityHash and
SpookyHash and switches the MurmurHash3 implementation to the x64
optimized one.

git-svn-id: https://pennmush.googlecode.com/svn/trunk@1764 ba372814-4f39-11de-9ad6-1127a62b9fcd