RFC on SDL_SetWindowPosition change to support moving window between monitors

This bug contains a patch that allows one to specify the SDL_WINDOWPOS_CENTERED(disply#) to the SDL_SetWindowPosition and have that function respect the display number to easily allow moving a window between monitors.


I would like some comments on the patch I provided for this as well as the change that it makes.

Edward Rudd
Skype: outoforder_cc