Partial fix to #195, added not implemented flag check

This is only a partial fix - previously our code didn't try to draw the border at all. Now it flashes properly when you open a window twice, but still doesn't when creating new windows.

It turns out that there is some original code in window_draw_widgets that wasn't decompiled at all for some reason (at least I can't see it anywhere). I've marked the places with missing implementations with comments.