[Ur] problems building Ur/Web on OS X since the change todynamic so libs

[Georg Bauer]

> Are you running Snow Leopard Georg? I had a problem with the MLton
> Compiler. Did you by chance run into this problem?

Yes, I did run into a problem with mlton on snow leopard, but that was
simple to fix - just some small patch I had to do, but can't for the
life of me remember what exactly it was. If you post error you get I
might remember what it was. I think it was just some deprecated
functions that required adding _XOPEN_SOURCE added to some header file
to allow the context switching functions to work again or something
like that.

bye, Georg