Reenable sdl_gfx code.

Why do I need sdl2_gfx? I don't, as I need the gfx operations on surfaces,
which is what v1 did. So use that instead. However, I had to do a "dirty" hack
to make this work: modify the gfx headers to include sdl2 headers instead of
sdl1.
Enable text input support with no unicode.

The input support has changed in SDL2 and it doesn't look straightforward to
update, so re-enable text input using sym instead of unicode, so at least I can
input something.