Fix #351: Python warnings in debugger code

Don't use inspect.getargspec on Python 2.

Close log file objects on exit.

Close os.devnull file objects on exit.

Close the listener socket used to get endpoints info from adapter.

Fix invalid escape sequences.

Run tests with Python warnings treated as errors.

Fix Django deprecation warning in test web app.

Work around pytest issues caused spaces in test names.

tests/debug/session.py

@@ -310,6 +310,7 @@ class Session(object):
             env.update(base_env)
 
         env["PYTHONUNBUFFERED"] = "1"
+        env["PYTHONWARNINGS"] = "error"
         env["DEBUGPY_TEST_SESSION_ID"] = str(self.id)
         env.prepend_to("PYTHONPATH", DEBUGGEE_PYTHONPATH.strpath)