Upgrading to Swift 1.2

[sendhil]

Merging work from #3554 and #3551. Thanks @nheagy and @alexcurylo for the hard work!

cc @astralbodies @jleandroperez

[jleandroperez]

I've added issue #3562 to review NSString <-> String interactions, and simplify when possible. I think some of those castings can be even removed, but let's tackle that in a different PR.

Looking great on my side!

[aerych]

Took this for a spin and it looks good to me. There is one breaking test, NSStringHelpersTest testEllipsizing, but I don't see how it is related to this changes here.
I agree with @jleandroperez on reviewing NSStrings <-> Strings, but, yeah, that can be in a different scope. :)

[alexcurylo]

That test broke for me in the Simulator too because CFStringTokenizerAdvanceToNextToken apparently suddenly started returning 0 when passed @"わたしはいぬがすきです". That seemed strange, so to test this against some other OS's and see if it was a real regression, I downloaded the 8.2 Simulator with 6.3.1 -- and that error went away! It also didn't show up running this branch through greenhouseci.com.