Add shift+P to profile once.

This restarts the interaction, and then reports the amount of time
it took to do so. This can give us an idea of how much (if any)
performance is being improved by the new screens code.
Fix all errors and warnings reported by pydev 3.5.

The predefinition directory (predef) needs to be added to the Ren'Py
interpreter in PyDev for this to work.
Store and use the cache of predicted screens.

This will generally let us show the screen a lot faster.
Update screens at most once per interaction.