pyoxidizer: add hooks to inject extra python packages and install files We need this type of hook to inject our internal extension and resource files at Google. Presumably this could be useful to others, so instead of trying to carry an internal patch we've done this in a modular way that should be of value upstream. I'm extremely puzzled by the behavior of glob() on Windows, and I'll be filing at least one (probably two) bugs upstream about it. Differential Revision: https://phab.mercurial-scm.org/D11092