Use relative URI in request line if :scheme is in http family

[icing]

• a recent change for when a ':scheme' header like 'https' was present on a non-TLS connection (or vice versa) made the request URI absolute. This was done to avoid loss of information.
• this change is now reverted or http and https schemes. Only when a non-http scheme is sent is an absolute URI used to forward that information.
• addresses #230 where it is pointed out that TLS terminations in front of Apache did not see absolute URIs in the past and would prefer to stick to that. The change did show up in access logs and cgi REQUEST_URI variables.