swift234

Only supersede initializers with other imported initializers when the types match.

This fixes a case where the Swift-variadic and C-varargs versions of
various initializers were superseding each other
<rdar://problem/16801456>.

It also uncovered some more cases where we weren't getting quite the
right semantics for factory-methods-as-initializers, which are also
fixed here.

Swift SVN r18010