swift234

Start allowing self.init/super.init calls to be forced with '!'.

Adjust our placement of RebindSelfInConstructorExpr to fall outside of
a force-value expression (!), allowing, e.g.,

  self.init(somethingThatCanFail: x)!

and

  super.init(somehtingThatCanFail: x)!

Start suggesting '!' when chaining/delegating to a failable
initializer from a non-failable one, in addition to suggesting that
the enclosing initializer become failable.

Note that DI cannot handle this yet, so this is only the Sema part of
rdar://problem/18497407.

Swift SVN r30219