Change get_current_ts to always use _Py_atomic_load_relaxed when available.
Created originally on Bitbucket by pantaloons (Michael McGee)
Was already merged in Bitbucket before import, marked as merged by the import user
Dropbox uses a modern version of the GIL with Python 2.7. This causes issues with this code, since we need to use _Py_atomic_load_relaxed without being Python 3.x
For all other situations, the behavior remains identical.