Merge remote-tracking branch 'remotes/kraxel/tags/pull-sdl-20141219-1' into staging

sdl2: fixes, cleanups and opengl preparation.

# gpg: Signature made Fri 19 Dec 2014 09:06:07 GMT using RSA key ID D3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>"
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>"
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>"

* remotes/kraxel/tags/pull-sdl-20141219-1:
  sdl2: Work around SDL2 SDL_ShowWindow() bug
  sdl2: Use correct sdl2_console for window events
  sdl2: move sdl2_2d_refresh to sdl2-2d.c
  sdl2: factor out sdl2_poll_events
  sdl2: add+use sdl2_2d_redraw function.
  sdl2: move sdl_switch to sdl2-2d.c
  sdl2: overhaul window size handling
  sdl2: move sdl_update to new sdl2-2d.c
  sdl2: turn on keyboard grabs
  sdl2: move keyboard input code to new sdl2-input.c
  sdl2: rename sdl2_state to sdl2_console, move to header file
  sdl: move version logic from source code to makefile

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>