Fixes for draw_background/sprite_tile functions

-Fixed draw_background_tile and draw_sprite_tile to not fail when
drawing with negative x and y.
-Fixed draw_background_area* functions. They were totally broken because
of wrong texture coordinates and wrong order of vertices (this might
also be a bug in the batcher, because the previous vertice order should
of still worked).
-Changed all floats to gs_scalars. This is just for consistency and
removes some warnings.