Fix mouse stuff in SDL.
Make SDL fail gracefully... so now it's SDL -> X11 -> Curses -> ANSI on *nix
I am no longer aware of *any* SDL issues... will enable as default after a
bit of cooking in CVS.

SDL-related stuff yet to do:
1) Deal with SDLMain.m correctly for OSX systems.
2) Add in support for SDL audio.
3) Test to see how much larger a binary with statically linked SDL is to
   decide if it's worth useing dlopen() and fallback ala X11.
4) Add Win32 SDL support.