Merge remote-tracking branch 'remotes/kraxel/tags/pull-sdl-20150312-2' into staging

misc ui patches, mostly sdl related.

# gpg: Signature made Thu Mar 12 14:51:07 2015 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-20150312-2:
  pixman: add a bunch of PIXMAN_BE_* defines for 32bpp
  Allow the use of X11 from a non standard location.
  configure: opengl overhaul
  sdl: Fix crash when calling sdl_switch() with NULL surface
  sdl: Refresh debug statements

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