Don't build libzfs_core if MK_ZFS == no

Sponsored-by: EMC Isilon
Signed-off-by: Garrett Cooper <yanegomi@gmail.com>
Unstaticize freebsd_trans_osrel for compat layer hacking

Signed-off-by: Garrett Cooper <yanegomi@gmail.com>
Trim down the base system a bit more

- Make bhyve and hast optional
- Remove ppp examples if MK_PPP == no

Sponsored-by: EMC Isilon
Signed-off-by: Garrett Cooper <yanegomi@gmail.com>

Conflicts:
	etc/rc.d/Makefile