make request_timeout and total_request_timeout account for connect phase

If a request is sent to a connection which isn't open, then the time to connect, usually covered by :connect_timeout, will also be account for in :request_timeout and :total_request_timeout. This is a potentially significant change of behaviour, which I think rectifies something that always catches peeps off-guard.

This was done by using a new connection callback, and set the timeout based on it for an incoming request if the connection is connecting?.

A previously unexistent check is performed so that only one type of timeout is set for a given request, while on the same connection.