Disable SSL test on versions of libcurl with blocking SSL handshakes.

(using gnutls instead of openssl and libcurl < 7.21.0).

tornado/test/httpserver_test.py

@@ -39,6 +39,13 @@ class SSLTest(AsyncHTTPTestCase, LogTrapTestCase):
         response = self.wait()
         self.assertEqual(response.body, "Hello world")
 
-if ssl is None:
-    # Don't try to run ssl tests if we don't have the ssl module
+if (ssl is None or
+    (pycurl.version_info()[5].startswith('GnuTLS') and
+     pycurl.version_info()[2] < 0x71400)):
+    # Don't try to run ssl tests if we don't have the ssl module (python 2.5).
+    # Additionally, when libcurl (< 7.21.0) is compiled against gnutls
+    # instead of openssl (which is the default on at least some versions of
+    # ubuntu), libcurl does the ssl handshake in blocking mode.  That will
+    # cause this test to deadlock as the blocking network ops happen in
+    # the same IOLoop as the server.
     del SSLTest