- Add exec hook "exec.created". This is called when the jail is

- Add exec hook "exec.created". This is called when the jail is
  created and before exec.start is called.			[1]
- Bump __FreeBSD_version.

This allows to attach ZFS datasets and various other things to be
done before any command/service/rc-script is started in the new
jail.

PR:			228066					[1]
Reviewed by:		jamie					[1]
Submitted by:		Stefan Grönke <stefan@gronke.net>	[1]
Differential Revision:	https://reviews.freebsd.org/D15330	[1]