prstreams has been updated

I just checked in an updated implementation of prstreams
by Fredrik Roubert of Google that is compliant to the
modern C++ standards:

https://bugzilla.mozilla.org/show_bug.cgi?id=581465

I will treat prstreams as the "contrib" code commonly
found in open source projects.  prstreams isn't officially
supported, but I will merge patches contributed by its
users.

I thank Fredrik Roubert for the contribution!

Wan-Teh Chang