Blender Git Loki

2.5

Cleanup of saving code for Image window.

Little extra: added poll() check for buttons, greying out inactive
menu items or buttons. You can see it work in Image menu.
(Item 'save image' is grey when it wasn't saved, then you have to
use the 'save as' item).

Carefully designing poll checks is worth a trial once. :)
Do note that cpu time for polls should be totally minimal.