Add very crude disk swapping.

Needs to be written more cleanly. Here as a POC.
Merge branch 'master' into cd-swap

Conflicts:
	mednafen/psx/psx.cpp
Add MKDIR defines.
Fix Win32 build.
Fix excessive printf stuff.
Merge branch 'master' into cd-swap
Fix segfault in PSX.
Merge branch 'master' into cd-swap
Fix Win32 build.
Merge branch 'master' into cd-swap
Merge branch 'cd-swap' of git://github.com/libretro/mednafen-libretro

Conflicts:
	mednafen/psx/psx.cpp
Update libretro.h.
Add replace/add interfaces for cdswap.