Fix plPythonPack Logic

This changeset fixes the bug that caused plPythonPack to produce a spurious ki.pak file.

That bug was caused by the fact that directories other than "plasma" and "system" were considered to be separate pack files (eg journal.pak). When python package support was added to the packer, the logic was not changed to ensure that only non-package directories were made into separate pak files. This oversight has been corrected by checking for the presence of __init__.py. If __init__.py is present, the folder is packed into python.pak. Otherwise, the original functionality of producing a separate pak file is retained.