Add an option to tell setup.py not to download dependencies

Traceback (most recent call last):
  File "/tmp/ve/bin/ibid-setup", line 4, in <module>
    import pkg_resources
  File "/tmp/ve/lib/python2.6/site-packages/setuptools-0.6c9-py2.6.egg/pkg_resources.py", line 2566, in <module>
    class cls(cls,object): pass
  File "/tmp/ve/lib/python2.6/site-packages/setuptools-0.6c9-py2.6.egg/pkg_resources.py", line 524, in resolve
    # Find the best distribution and add it to the map
pkg_resources.DistributionNotFound: wokkel==0.4

That's a result of hitting ^C