Hashing Algorithm usage

MD5 has been totally deprecated for usage when collisions may be an
issue - we should migrate to SHA-1 going forward.

SHA-1 isn't the best choice either - it's relatively performance hungry
since it is designed to be cryptographically secure.  Something like
Murmurhash3 would be much more desirable (and it is 128-bits).  But
SHA-1 is the best choice of the built-in PHP hash algorithms.