swift234

Test: Emulate deployment on older OSes to test weak linking to Objective-C

These tests emulate deploying back to an older OS where newer APIs are not
available by linking to an Objective-C framework where APIs have been
annotated to only be available in the far future and then moving the famework
aside so that it can't be found at run time.

These tests include some basics (global variables and classes), but the focus
is on Objective-C protocols to validate the change allowing types to
conform to protocols less available than the types themselves.

Swift SVN r30005