This is a quick-fix release to take care of the following issues:
Fixed a probably rare, but fatal bug on OSX when calling certain overloaded virtual methods with implementations in Python.
Fixed char pointers in generated stub code to have a valid pointer value.
Reverted the change that loads up install_requires from the contents of requirements.txt. Split the requirements.txt file into one for install and one for development.
This is a companion discussion topic for the original entry at https://wxpython.org/news/2019-05-21-wxpython-406-release/index.html