logger: permit to send messages larger than 1024 characters

logger: permit to send messages larger than 1024 characters

This is an important capability that has been specified in RFC5424.
However, messages larger than 1024 chars are being accepted for years
now by at least rsyslog and syslog-ng.

This patch adds the option --size to permit setting a new max
size, with 1024 being the default.

Note that the size limit is only approximative, as we do not take the
header size in account (RFC talks about total message length).

[[kzak@redhat.com: - add 'S' to getopt_long(),
                   - rename --message-size to --size
                   - add the option to bash-completion]

Signed-off-by: Karel Zak <kzak@redhat.com>