[physfs] doxygen does not generate all manpages anymore

[Ryan C. Gordon]

> Hm then install it :D

I just installed Doxygen.

The manpages are largely empty because they just link back to physfs.h 
... frankly, I haven't been thrilled with Doxygen. I'll probably figure 
out a replacement for it. If you set "MAN_LINKS = NO" in the Doxyfile, 
though, it'll get rid of all those extra manpage files (leaving one for 
physfs.h and some of the structs, but not the functions...odd).

Also, the patch that adds '\' chars to negative values doesn't seem to 
be necessary: they show up (in HTML and manpages) as "\-1" instead of 
"-1". This is with Doxygen 1.6.3. I'm backing out that patch.

--ryan.