[physfs] Impending PhysicsFS 3.0.0...

[Ryan C. Gordon]

> I have a question regarding PHYSFS_enumerate, or rather the callback 
> signature. How about turning that callback return value into an enum 
> with names such as "PHYSFS_CONTINUE/STOP/ERROR"?

Yeah, that's a good idea. I think it was sheer laziness on my part that 
prevented that.

I've changed this here:
https://hg.icculus.org/icculus/physfs/rev/97d3641bfba3

Now returns a PHYSFS_EnumerateCallbackResult instead of an int, which is 
either PHYSFS_ENUM_ERROR, PHYSFS_ENUM_STOP, or PHYSFS_ENUM_OK, but 
otherwise works as before.

--ryan.