[physfs] PalmOS support

[Brian Hook]

My intent wasn't that it makes it easier to write the Palm game as 
much as it makes it easier to stay portable between the two.

If all your code uses PHYSFS, then on PalmOS you're suddenly punting 
back to a native layer instead of continuing with PHYSFS.  If you can 
just load a resource as a ZIP and then all your remaining PHYSFS code 
remains the same, then I'd think that's a win.

Brian