swift234

implement <rdar://problem/17013042> T! <-> T? conversions should not produce a diamond

Two pieces to this:
 - Peephole OptionalEvaluationExpr(InjectOptionalExpr(BindOptionalExpr(X))) to 
   bitcast x to the result type.
 - Enhance OptionalEvaluationExpr to delete the failure block if not needed.

This is the same as r28111, except that we finalize the initialization in the
address-only case.  A reduced testcase for the specific issue is added to
optional-casts.swift.



Swift SVN r28150