Document another configuration use case for the use of `__force_dict__`.

Change-Id: I74ab3b38adad456440df728d54843bbcbbad1ee3
Fixes bug: 1293545
Delay the `threading.local` import to allow for eventlet/gevent monkeypatching.

Fixes bug 1294177

Change-Id: I51482148602d85e40230547d0e19cf0c2a0c6d8a
Merge "Document another configuration use case for the use of `__force_dict__`."