Hashing on the bytes instead of the words does
a (much) better job of using all the bits, so that
maps of floats have linear performance.
LGTM=khr
R=golang-codereviews, khr
CC=adonovan, golang-codereviews
https://golang.org/cl/126720044
The implementation 'return 0' results in too many collisions.
LGTM=khr
R=golang-codereviews, adonovan, khr
CC=golang-codereviews, iant, khr, r
https://golang.org/cl/125720044