Fixes #20. Make sure the manifest_maker monkeypatch only occurs once and that it gets all its required locals encapsulated. This is why I hate any sort of monkey-patching, but it appears to be the only way to get this feature working.

git-svn-id: https://svn.stsci.edu/svn/ssb/stsci_python/d2to1/trunk@23570 fe389314-cf27-0410-b35b-8c050e845b92