Always create pid file if --pidfile command line option is provided.
Have a pid file can be useful when not running daemon mode. For example, when running under a process supervisor it can be handy to look at the pid file as if Suricata was running as a daemon.
I suggest always creating a pid file if the --pidfile command line option is provided. The proposed pull request (https://github.com/inliniac/suricata/pull/907) does not change any behaviour for users who daemonize Suricata. For users who run in the foreground, Suricata will no longer exit if the --pidfile option is provided, instead the pidfile will be created.
Note: The pid-file option in the configuration file still only applies when running as a daemon. This prevents Suricata from behaving any differently than before.