Rework module finding and filtering in `fusil-python-threaded`

[devdanzin]

Currently fusil-python-threaded module finding is a hack in ListAllModules.search_modules, depending on a patched pkgutil.py and not allowing filtering of files. We should:

• Revert to pkgutil.iter_modules and avoid needing a patched pkgutil.py.
• Revert to matchModule to filter modules, fixing it if necessary.
• Make sure search_modules returns the same modules as pkgutil.walk_modules would.
• Make sure --only-c, site-packages and the blacklists work correctly.

[devdanzin]

Done in 011eefd and 55c626c.