build of mac package fails due to pkgutil in zetuptoolz

[zooko]

​http://allmydata.org/buildbot/builders/Mac%20OS-X/builds/1039/steps/mac_exe/logs/stdio

  File "/System/Library/Frameworks/Python.framework/Versions/2.5/Extras/lib/python/modulegraph/modulegraph.py", line 114, in find_module
    if isinstance(importer, pkg_resources.ImpWrapper):
AttributeError: 'module' object has no attribute 'ImpWrapper'

This has something to do with the fact that the version of zetuptoolz bundled with TahoeLAFS in misc/dependencies, called 'setuptools-0.6c12dev' replaced pkg_resources with the new pkgutil module, and modulegraph apparently uses pkg_resources. Why modulegraph's use thereof results in this incompatibility I haven't figured out yet. I have tested a version of zetuptoolz which uses the old pkg_resources style instead of the new pkgutil style -- ​http://allmydata.org/trac/zetuptoolz/changeset/20090703214517-92b7f-126e534865d9104679dc424aa681cf26a26f2921 -- and shown that this error goes away with that zetuptoolz (this is why this failure doesn't happen on ootles the way it does on the "OS X" (VirtualZooko) builder). So a good solution to this ticket would be to upgrade our bundled zetuptoolz to that new version of zetuptoolz. Although it would be nice to understand more precisely why it doesn't work this way -- maybe we could submit a patch to some other project to help.