After late parsing an objc method, make sure there are no leftover cached tokens,

because the memory associated with them is going to get released.
We also don't want them to affect later parsing.
(We do the same for C++ inline methods.)

The underlying cause for the leftover tokens is going to be addressed in the
next commit.

Couldn't get a test case for the crash though. rdar://10583033.

llvm-svn: 146814