BOARD-patches/sdl2: force window focus(kbd/mouse) and restrict mouse x/y

[Apaczer]

Two patches for SDL2:

• remove GOTFOCUS/LOSTFOCUS events from SDL_DirectFB code, because SDL for real have no idea when it happens with mouse mv, state becomes impossible to check if no-cursor is active and smbd check mouse-hover over window in SDL
• restrict mouse move in SDL_mouse code to only screen dimmension, otherwise cursor endups travelling to infinity (same happens in df_input example strangely, but no issue in df_window).

This of course will brake multi app usage via SDL backend because all windows will receive the same input events at the same time (funny cuz I tested vanilla sdl and same thing happens), but I don't expect anyone to make any use of that feature in forthcoming future (it is still valid to use multi window via pure directfb).

Tested dethrace and opentyrian, all seems ok and works similary to directfb in sdl1.2