Rename PFObject '_state' instance variable to '_pfinternal_state'.

[richardjrossiii]

This is only a temporary workaround. We should go back and clean up, not only our uses of the '_pfinternal_state' ivar directly, but also discuss whether our auto property synthesis still makes sense to have as a feature.

This prevents conflicts with our automatic property synthesis that is done for registered subclasses.

[nlutsenko]

This works, but I am slightly skeptical on usage of double-underscores, since it's reserved by Apple.
It doesn't interfere with this, but definetly is something to be aware of.

@richardjrossiii Can we have a test for this, pretty please?

[richardjrossiii]

Will write test, and change from double underscore. Stay tuned...

[nlutsenko]

Still using double underscores for __pfinternal, do you think it's required?
Probably we can simply use _pfinternal_state, I don't think anyone is likely to use snake-case as well as prefix with pfinternal :D

[richardjrossiii]

We already reserve fields in parse starting with _, so no, I guess the double underscore isn't necessary. I don't have any strong feelings either way, especially considering this is just a short-term workaround.

Will go with your lead and use _pfinternal_state.

[nlutsenko]

LGTM, ship at will after nit is fixed.