[physfs] Fix PhysicsFS 1.0.2 build error on Mac OS X

[Ryan C. Gordon]

> PhysicsFS 1.0.2 fails to build on Mac OS X 10.4.11 with the following 
> error message.
> 
> +      LIBS="-lreadline -lcurses $LIBS"

We're probably not going to do another 1.0.x release, so it's not worth 
fixing this properly (2.0 doesn't use configure.in anymore), but this 
patch would make PhysicsFS itself depend on readline, when it's just an 
optional feature of the test program.

I'm not sure why Mac OS X is ignoring the BUILD_READLINE setting, but 
it's probably another esoteric automake quirk. It's why we moved to CMake.

I would encourage you to move to PhysicsFS 2.0, but if you have to use 
1.0 for any reason, you can run configure with --disable-readline on Mac 
OS X (or perhaps: LDFLAGS="-lreadline -lcurses" ./configure ...)

--ryan.