swift234

Fix a multitude of issues with extensions exposed to Objective-C (r19116).

- Category names weren't unique.
- We were using an attribute to detect if something was a Swift category,
  but attributes can't be used on categories.
- The test that this was all working was failing in a way that wasn't caught.

To solve these problems:

- We're using a macro to generate category names based on __LINE__ in addition
  to the current module.
- The importer uses the macro to detect that the category comes from Swift
  (no attribute needed).
- The test now has a deliberate error for -verify to catch.

<rdar://problem/17342287&17538553>

Swift SVN r19479