setup: remove a couple of horrible work-arounds in setup.py now that we rely on our...

setup: remove a couple of horrible work-arounds in setup.py now that we rely on our own toothpick of setuptools which fixes those issues
also specify that we need our latest revision (11dev) of our toothpick of setuptools
also *always* setup_require setuptools_darcs at module import time.  Formerly we added setup_require setuptools_darcs only if the PKG-INFO file were not already created.  There is some weird, irreproducible bug to do with setuptool_darcs, and I guess that the fact that whether it is required or not depends on that autogenerated file might have something to do with it.  Anyway, this is simpler.