Stop HttpRequest and AccessLogEntry memory leaks.

Stop HttpRequest and AccessLogEntry memory leaks.

The leaks were introduced by recent request_header_add improvements (r12213)
which needed server-side access to client-side information like client
certificate so that it can be stuffed into the outgoing request headers.
Stuffing was done via Format API that uses AccessLogEntry as the source of
information.

This change breaks the HttpRequest->AccessLogEntry->HttpRequest refcounting
loop that prevented both request and ale objects from being destroyed. The ale
object is now delivered to the server side using FwdState::Start() API.  Only
HTTP code currently takes advantage of ale availability on the server side.

Also had to modify httpHdrAdd() API because ale is no longer available via
the request pointer.