swift234

Generalize the @noescape attribute to be a type attribute allowed
in arbitrary places.  This fixes a regression caught by SR-770 that
would otherwise be introduced by us removing automatic currying syntax,
it allows the use of @noescape on typealiases (resolving SR-824),
allows @noescape on nested function types (fixing rdar://19997680)
and allows @noescape to be used on local variables (fixing
rdar://19997577).

At this point, @noescape should stop being a decl attribute, but I'll bring
that up on swift-evolution.