logger: warn when --file and command line message are combined

When --file is combined with command line arguments the later has
silently been ignored.  This commit makes user to be aware the logger
will not use command line arguments when --file is specified.

Reported-by: "Daniel 'DaB.' Baur" <debian@daniel.baur4.info>
Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=467244
CC: Andreas Henriksson <andreas@fatal.se>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
logger: add hostname to rfc3164 message

This makes the obsolete protocol a little bit more compliant with the
internet standard, while few should care.  Sending messages using rfc5424
format is better, because for example the rfc3164 dictates hostname must
not be fully qualified.

Reported-by: Frank Thilo <thilo@unix-ag.org>
Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=705217
CC: Andreas Henriksson <andreas@fatal.se>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>