independent SES_RxReq() function.

Eliminate timeout_req and rely on timeout_idle to do the job.
(Length of this timeout still under debate on -dev)

out of http1_wait()

panic.clear gains a -z optional parameter.

Fixes #1609.

Fixes #1693.

It might contain non-printable chars.

matter what protocol, a request is quite likely to happen soon-ish.

(for lack of any better place) since they will become involved in
protocol switching.

Complain about unrecognized protocols.

Presently we have two switch points:

  Created/Waited session and
  Rescheduled (from waiting list) request.

In the future we will need to tell what protocol controls a give
session, for instance when we come back from the waiter or waiting
list.   Rather than spend memory on a dedicated field for this,
protocols will share the enum sess_step, and ranges will be used
to dispatch to protocols.

central include files (like <common/common.h>) to specific source files.

purpose never materialized and it causes massive <errno.h> polution.