Including config.h is necessary to get e.g. the _GNU_SOURCE define and
any other definitions that autoconf declares. Hence, config.h needs to
be included as the first header in each file.
This is done either via:
1. Including "common.h" (i3bar)
2. Including "libi3.h"
3. Including "all.h" (i3)
4. Including <config.h> directly
Also remove now-unused I3__FILE__, add copyright/license statement
where missing and switch include/all.h to #pragma once.
Receiving EOF from a client is not an error, but rather a standard way a
client may disconnect from the IPC. This should rather be logged from
a consumer of the libi3 ipc_recv_message() function as a normal client
disconnect event.
fixes#1252
Michael Stapelberg