The new 'Terminal_session::size_changed_sigh' RPC function registers a
signal handler that is triggered each time when the terminal size
changes. It enables the client to adjust itself to the new size by
subsequently calling the 'size' RPC function. Of all terminal servers,
only the graphical terminal triggers this signal.
To better support non-blocking terminal components, let the
'Terminal::Session::write()' function return the number of bytes
actually written.
Fixes#2240
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082
