Fix the following error. Looks like we have to have a function to call
for the entrypoint.

$ pip install dist/sshuttle-0.76.dev8_ngf59508f4-py2-none-any.whl
Processing ./dist/sshuttle-0.76.dev8_ngf59508f4-py2-none-any.whl
Installing collected packages: sshuttle
Exception:
Traceback (most recent call last):
  File "/tmp/ddd/local/lib/python2.7/site-packages/pip/basecommand.py", line 211, in main
    status = self.run(options, args)
  File "/tmp/ddd/local/lib/python2.7/site-packages/pip/commands/install.py", line 311, in run
    root=options.root_path,
  File "/tmp/ddd/local/lib/python2.7/site-packages/pip/req/req_set.py", line 646, in install
    **kwargs
  File "/tmp/ddd/local/lib/python2.7/site-packages/pip/req/req_install.py", line 803, in install
    self.move_wheel_files(self.source_dir, root=root)
  File "/tmp/ddd/local/lib/python2.7/site-packages/pip/req/req_install.py", line 998, in move_wheel_files
    isolated=self.isolated,
  File "/tmp/ddd/local/lib/python2.7/site-packages/pip/wheel.py", line 479, in move_wheel_files
    maker.make_multiple(['%s = %s' % kv for kv in console.items()])
  File "/tmp/ddd/local/lib/python2.7/site-packages/pip/_vendor/distlib/scripts.py", line 364, in make_multiple
    filenames.extend(self.make(specification, options))
  File "/tmp/ddd/local/lib/python2.7/site-packages/pip/_vendor/distlib/scripts.py", line 353, in make
    self._make_script(entry, filenames, options=options)
  File "/tmp/ddd/local/lib/python2.7/site-packages/pip/_vendor/distlib/scripts.py", line 244, in _make_script
    script = self._get_script_text(entry).encode('utf-8')
  File "/tmp/ddd/local/lib/python2.7/site-packages/pip/wheel.py", line 396, in _get_script_text
    "import_name": entry.suffix.split(".")[0],
AttributeError: 'NoneType' object has no attribute 'split'