'Called every time a header is received. Stores the header information
as key-value pairs in the C{headers} attribute.
@type key: C{str}
@param key: An HTTP header field name.
@type value: C{str}
@param value: An HTTP header field value.'

def handleHeader(self, key, value):

    key = key.lower()
    l = self.headers.setdefault(key, [])
    l.append(value)
