This function is a part of Readline interface for a long time
(with a different type).

The BIRD client code is restructured that most of the code (including
main function) is shared in client.c, while birdc.c and birdcl.c contain
just I/O-specific callbacks. This removes all duplicated code from
variant-specific files.

Renames some files:
birdc/client.c -> birdc.c
birdcl/client.c -> birdcl.c
client_common.c -> common.c

Fix handling of async messafe in the bird light client. The async message
may occure at the any moment so we need the client to liste for the
message from server when it waits for user input.

Fix handling of questionmark handling in the bird light client. The
questionmark should display help when it is the last non-blank character on
command line. Otherwise the questionmark does not have any special meaning
and it could be a part of a pattern.

Restructure client/ subdir. Add two different flavors of client.
The full featured birdc client code is in client/birdc/.
The new light client birtcl is in client/birdcl/.
Common sources of both clients are directly in client/.

Rework on-line auto-completion in client/command.c to conditionally turn off
ncurses-specific code.

Add lightweight client without libreadline and ncurses dependencies - birdcl.
The birdcl lacks support of history, on-line auto-completion and there
are different implementations of "more" functionality and help on '?' press.
New client operates in canonical terminal mode (apart from "more" display)
and therefore all commands have to be executed by a return key including help
commands (called by '?' character in the end of the line).
Apart from these limitations the interaction style should be the same as
for the full client - birdc.
Build of birdcl is always on (independent on --enable-client parameter).

Pull out routines for interacting with the server and interpreting
internal commands which are not dependent on libreadline and
ncurses libraries.

This is a preparation step for a new lightweight birdc client.

Rename client/client.c to client-full.c and change the Makefile accordingly.
This is a preparation step for introducing a new lightweight client which
should reuse as much code as possible from the old one but it should not depend
on external libraries.
Signed-off-by: Tomas Hlavacek <tmshlvck@gmail.com>

Also adds support for executing commands using birdc <cmd>.

Also does some code restructuring.

shows only parts of larger outputs (for example 'show route all').
It seems that birdc reads (from bird) and writes (to stdout)
everything but during execution of some readline code some already
written output disappeared (although it is fflush()ed and
tcdrain()ed).

As birdc reads from stdin when select said there are some data,
O_NONBLOCK for stdin is unnecessary and when it is removed,
i didn't notified this problem.

in select loop.

for even only medium sized route table output. Fix a strange garbled
output problem in the client. The latter seems to be caused by some
library doing tcflush while there is still command output pending. So
the best fix here is to do fflush and then tcdrain. Note that this
problem occurs only under certain load situations and is not too easy to
reproduce.

(by Andreas)

with connection to clients on libc5 machines.

the user to press `?' if he wants help.