Put close /para tag around itemizedlist. This fixes problem where there

Put close /para tag around itemizedlist.  This fixes problem where there
is a blank line before the list, but no blank line after list and before
next line. It looks strange and was noticed in printed FreeBSD Handbook.
Now there is a blank line after list too.  I am not sure if this correct
fix so please let me know if there is a better way.

Instead of saying /usr/local/etc/rc.d startup system, just say
rc.d startup system.

Change reference to STABLE to PREVIEW.

Todo:
 show DragonFly example for compat.linux.osrelease sysctl.