Simple fixes for more strict warnings enabled about comparisons.
More unsigned -> signed compares
Another comparison
More compares
Last of compares in rtlib
Some unsigned -> signed compares in gfxlib
More gfxlib comparisons
Finished finding signed/unsigned compares (linux)
Fixed: fb_GfxImageInfo was performing ptr math on a void ptr
gfxlib2: Fix SCREEN_EXIT declaration rather than every use
rtlib: Fix FB_STRSIZE() signedness (FBSTRING.len is signed too)
rtlib: Fix FB_WEOF signedness
gfxlib2: Fix FB_NAN declaration rather than every use
rtlib/gfxlib2: Better fixes for some previously fixed signedness issues

(I hope they really are better)
gfxlib2: Remove useless >= 0 check on unsigned var
rtlib/gfxlib2: Fix more signedness warnings in win32 build
Merge branch 'fix-signed-unsigned-compares'
makefile: Always use -Wextra for C code
rtlib/gfxlib2: Fix missing initializers because MinGW gcc complains
dos gfxlib2: Store __dpmi_allocate_ldt_descriptors() result in signed int