Allow the cf_returns_[not_]retained attributes to appear on out-parameters.

Includes a simple static analyzer check and not much else, but we'll also
be able to take advantage of this in Swift.

This feature can be tested for using __has_feature(cf_returns_on_parameters).

This commit also contains two fixes:
- Look through non-typedef sugar when deciding whether something is a CF type.
- When (cf|ns)_returns(_not)?_retained is applied to invalid properties,
  refer to "property" instead of "method" in the error message.

rdar://problem/18742441

llvm-svn: 240185