Add Python 2.3 support

This commit also adds the 'six' dependency

vcr/stubs/compat.py

@@ -0,0 +1,43 @@
+import six
+from six import BytesIO
+from six.moves.http_client import HTTPMessage
+try:
+    import http.client
+except ImportError:
+    pass
+
+
+"""
+The python3 http.client api moved some stuff around, so this is an abstraction
+layer that tries to cope with this move.
+"""
+
+def get_header(message, name):
+    if six.PY3:
+        return message.getallmatchingheaders(name)
+    else:
+        return message.getheader(name)
+
+
+def get_header_items(message):
+    if six.PY3:
+        return dict(message._headers).items()
+    else:
+        return message.dict.items()
+
+
+def get_headers(response):
+    if six.PY3:
+        header_list = response.msg._headers
+        return [b': '.join((k.encode('utf-8'), v.encode('utf-8'))) + b'\r\n'
+                 for k, v in header_list]
+    else:
+        return response.msg.headers
+
+def get_httpmessage(headers):
+    if six.PY3:
+        return http.client.parse_headers(BytesIO(headers))
+    msg = HTTPMessage(BytesIO(headers))
+    msg.fp.seek(0)
+    msg.readheaders()
+    return msg