Merge PR174: depend unconditionally on txtorcon

This adds no additional dependencies (txtorcon only depends on things that we
already depend upon anyways), and txtorcon itself is only 300kB. This removes
the need for using `pip install magic-wormhole[tor]` to get Tor support:
instead, just dod `pip install magic-wormhole`.

closes #174

setup.py

@@ -36,11 +36,11 @@ setup(name="magic-wormhole",
           "click",
           "humanize",
           "ipaddress",
+          "txtorcon >= 0.19.3",
       ],
       extras_require={
           ':sys_platform=="win32"': ["pypiwin32"],
-          "tor": ["txtorcon >= 0.19.3"],
-          "dev": ["mock", "tox", "pyflakes", "txtorcon >= 0.19.3"],
+          "dev": ["mock", "tox", "pyflakes"],
       },
       test_suite="wormhole.test",
       cmdclass=commands,