[physfs] Build issues with physfs 2.0 / HG

[Ryan C. Gordon]

> Also I have a diff like so to get the readline support
> to build. It checks for a libhistory which we don't
> have but it doesn't actually use said library.

I think the historical (hah!) reason is that on GNU/Linux, readline 
required libhistory to function, or something. If I'm even remembering 
correctly, it would have been true over a decade ago.

--ryan.