Remove Connection: close header for 501 error handling rest

Ralf doesn't know why the "Connection: close" header was added. Was
there since the original code to support OPTIONS verb was added.
He agrees it can be removed.

Enable test for that code path.

Author: rouilj

test/test_liveserver.py

@@ -70,10 +70,8 @@ def test_start_page(self):
         self.assertTrue(b'Creator' in f.content)
 
 
-    def disable_test_http_options(self):
+    def test_http_options(self):
         """ options returns an unimplemented error for this case."""
-        '''note this currently triggers an assertion failure in the
-           python wsgi handler, so disable while investigating'''
 
         # do not send content-type header for options
         f = requests.options(self.url_base() + '/',