Fix to allow using SDL when compiling with v110_xp or v120_xp -- compiling with VS2012/VS2013 with the XP targeting option.
In order to ensure that we can target Windows XP we compile with the v120_xp toolset instead of v120. This means that we use an earlier SDK version and it means that winapifamily.h is not available. Compiling for this old SDK can be detected using the _USING_V110_SDK71_ define which is set through the %(PreprocessorDefinitions) option.
SDL 2.x recently accepted patches to enable OpenGL ES 2 support via Google's ANGLE library. The thought is to try to eventually merge SDL/WinRT's OpenGL code with SDL-official's.
If the app is in landscape mode and the user presses the power button, a pause
is followed immediately by a surfaceChanged event because the lock screen
is shown in portrait mode. This triggers a "false" resume.
So, we just pause and resume following the onWindowFocusChanged events.
Also, wait for SDL_APP_WILLENTERBACKGROUND and SDL_APP_DIDENTERBACKGROUND before
blocking the event pump.