Enable strict warnings in test runs.

This includes python 3.2's ResourceWarnings, which exposed the
socket leaks fixed in the previous commit.

tornado/test/runtests.py

@@ -29,5 +29,19 @@ def all():
     return unittest.defaultTestLoader.loadTestsFromNames(TEST_MODULES)
 
 if __name__ == '__main__':
+    # The -W command-line option does not work in a virtualenv with
+    # python 3 (as of virtualenv 1.7), so configure warnings
+    # programmatically instead.
+    import warnings
+    # Be strict about most warnings.  This also turns on warnings that are
+    # ignored by default, including DeprecationWarnings and
+    # python 3.2's ResourceWarnings.
+    warnings.filterwarnings("error")
+    # Tornado shouldn't use anything deprecated, but some of our
+    # dependencies do (last match wins).
+    warnings.filterwarnings("ignore", category=DeprecationWarning)
+    warnings.filterwarnings("error", category=DeprecationWarning,
+                            module=r"tornado\..*")
+
     import tornado.testing
     tornado.testing.main()