Fix <rdar://problem/6697053> instance variable is protected.

Treat @package the same as @public. The documentation for @package says it is analogous to private_extern for variables/functions. Fully implementing this requires some kind of linker support (so access is denied to code outside the classes executable image). I don't believe GCC fully implements this semantic. Will discuss with Fariborz offline.

llvm-svn: 67755