Many of our afw pybind11 wrappers are rejected by pybind11 2.2.3. In a few cases these appear to be actual errors, e.g. see http://pybind11.readthedocs.io/en/stable/upgrade.html and https://github.com/pybind/pybind11/issues/1052 but in most cases it appears to be that pybind 2.2.3 is pickier than 2.1.1.
This ticket is intended to make afw compatible with pybind11 2.2.3 while retaining compatibility with 2.1.1. Thus it will build with warnings under pybind11 2.2.3, and some modules show warnings when imported.