Replacing the exclusive_lock_function, shared_lock_function and unlock_function attributes with the acquire_capability and release_capability attributes. The old spellings will continue to work, but the underlying semantic attributes have been replaced.

Downgraded the capability diagnostics from error to warning to match the desired behavior, and updated the existing test cases.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204350 91177308-0d34-0410-b5e6-96231b3b80d8