swift234

Treat imported initializers from Objective-C protocols as 'required'.

Initializers for non-final classes will soon need to be 'required' to
conform to an initializer requirement in a protocol, so start
marking imported initializers from Objective-C protocols as
'required'. This is part of <rdar://problem/17408284> and
<rdar://problem/17415607>.

Swift SVN r20428