criu --help: print extended help in one call

This patch reformats the source to print extended help using just one
pr_msg command. Having it this way is easier to do further edits.

I have checked ./criu --help output before and after to make sure it's
the same.

Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>