This to avoids build conflicts with libc++ on FreeBSD, these __ prefixed values
are reserved for compilers. I apologize to anyone who has patches or branches
and has to go through the pain of merging this change, it may be easiest to do
these same replacements in your code and then apply/merge the patch.
Ref T37477.
OSL noise() function is generating NaN's in certain cases, fix for that goes to our
OSL branch.
Also add missing minimum weight and max closure checks to OSL, forgot to add these
when fixing another bug.