Add test case for Objective-C 2.0 properties bug

Add test case for Objective-C 2.0 properties bug

In a previous commit (f2d45e3) I noted what appears to be a bug in either the
Objective-C 2.0 properties implementation (spurious compiler warnings) or in
its documentation.

I've prepared this test case demonstrating the problem. In the course of doing
so I discovered that the problem has a workaround that is considerably easier
than I originally thought, and the bug doesn't actually make it impossible to
use the public-readonly/private-readwrite property pattern. I will apply the
new workaround in a subsequent commit.

Signed-off-by: Wincent Colaiuta <win@wincent.com>