swift234

Initial support for the @NSCopying attribute on properties.  This is enough to
wire it up, do basic semantic analysis and code gen a simple case of it.  There is
more type checking work to come, so it isn't complete yet.

This is the first step to:
<rdar://problem/15864836> Need a @NSCopying attribute for Cocoa types that aren't manually bridged



Swift SVN r16345