Fix PyDev 3.6.0 errors.
Fix more PyDev 3.6.0 warnings.
When putting a screen into the old state, make a copy.
Make _current_screen valid during per_interact() and render().

This let's us defer decisions about the current screen until
closer to render time.
Make XScrollValue and YScrollValue use the current screen.

This lets them deal with cases where they are reused on a copied
or hiding screen.
sl2: Ensure screen.widgets is updated on reuse.
Merge remote-tracking branch 'upstream/master'