Absolutely horrible default string hashing

[dsimcha]

== Quote from bearophile (bearophileHUGS at lycos.com)'s article
> dsimcha:
> > we first need to fix D's string hashing.<
> Ages ago I did suggest this one in the main D newsgroup:
> http://www.azillionmonkeys.com/qed/hash.html
> Bye,
> bearophile

Yeah, upon further reverse engineering, the way string hashing "works" is that it
simply adds up all the character code values of the characters and returns this
sum.  The implementation is in

dmd\src\druntime\src\compiler\dmd\typeinfo\ti_AC.d ,

and I've verified this both by reading the code and by implementing the same thing
myself and seeing if the results are the same.  If anyone has a better way to do
it (which would be almost anything; I've written a few myself, although they are
extremely simplistic and I'm sure anyone who actually knows what they're doing
could do even better), please submit a patch.  I've filed this as bug 2922,
because it's a severe performance issue, so please submit there.