Header keys should always be lower case.

I actually can't find anywhere in the standard that mandates this, but
the static header table uses entirely lower-case keys. To avoid
inefficiency in sending the headers, just force people to use lower-case
versions.

Author: Lukasa

hyper/http20/stream.py

@@ -78,7 +78,7 @@ def add_header(self, name, value):
         """
         Adds a single HTTP header to the headers to be sent on the request.
         """
-        self.headers.append((name, value))
+        self.headers.append((name.lower(), value))
 
     def send_data(self, data, final):
         """

test/test_hyper.py

@@ -838,7 +838,7 @@ def test_streams_can_have_headers(self):
     def test_stream_opening_sends_headers(self):
         def data_callback(frame):
             assert isinstance(frame, HeadersFrame)
-            assert frame.data == 'TestKeyTestVal'
+            assert frame.data == 'testkeyTestVal'
             assert frame.flags == set(['END_STREAM', 'END_HEADERS'])
 
         s = Stream(1, data_callback, None, NullEncoder, None)