Make update_package_files future-proof

`update_package_files` keeps growing new keyword arguments.  To prevent affiliated packages from needing to update their `setup.py` files on a regular basis, it has been replaced with `get_package_info` which returns a dictionary suitable for use as keyword arguments to `distutils.setup`.  The old update_package_files is still around for backward-compatibility, but displays a `DeprecationWarning`.