Fixes portrait pause behavior.

The game pauses in portrait mode because game elements may not fit.
The old strategy didn't work all the time, and it didn't tell the
player why the screen went black. Given that portrait is a common
orientation for those with smartphones, I don't want players who
get a black screen to turn away thinking the game doesn't work. The
reminder to turn the device sideways is important.

If you're using an LCD in portrait mode, I apologize. No resolution
detection yet, I'm afraid.