[boost] [hash] Type trait for hash functions that are well distributed.

Hi, I'm thinking about adding a type trait for hash functions to indicate if it's appropriate to use them with a "power of 2" hash table. This would let hash tables be more efficient when using an appropriate hash function, especially when compiling for 64 bit. Any thoughts on how this should be designed? I have a rough design in mind (similar to the allocator_traits propagation traits), but would like to hear other's ideas first. thanks, Daniel