[physfs] Fix compilation on OS X 10.7

[Ryan Schmidt]

Hi, physfs 3.0.1 fails to build on OS X 10.7 with the latest version of clang available in Xcode on that platform:


error: expected method to read array element not found on object of type 'NSArray *'
        NSString *path = (NSString *) paths[0];
                                      ^
1 error generated.


The fix is here:

https://trac.macports.org/attachment/ticket/56077/patch-physfs-objectatindex.diff


Thanks.

-Ryan