sdl-gui: fix input speed issues by setting vsync

several games had issues with input speed:
- games using keyboard got several keystrokes instead of one
- games using mouse or even just the workbench wouldnt register
  double-click as such, since with the fast input processing those
  clicks would seem to distant in time.

closes #36
sdl-gui: fix setting/display of CPU parameters

both cpu speed and cpu type options displayed bogus values and didnt
work (were not implemented).

unfortunately setting CPU to max causes input speed problems to re-
appear (fixed in parent commit for real speed).
Merge pull request #48 from rofl0r/sdlgui_polish

sdl-gui polish