Here are basic instructions for migrating from 20071229 (or any older
verison before that date) to 20080207 (or any newer version after that date)
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1. Mode handler 'action' is junked.  I didn't like having commands in the
config that didn't match how nsh was used on the command line.

pf action
 enable
 reload

turns into:

pf enable
pf reload

2. Vlan configuration now has more words:

vlan 44 fxp0

turns info:

vlan 44 parent fxp0

I did this because I added another keyword, priority.  It makes the
resulting config easier to read.

3. If you try to convert the config by installing the new nsh binary,
running 'write' and rebooting, you'll fail.  Nsh now looks for
/var/run/pf.conf.enabled to specify the 'pf enable' and 'pf reload'
keywords.  So, before you run nsh, run 'write', and reboot, create
an empty /var/run/pf.conf.enabled file first.  Then nsh will know
to specify 'pf enable' in the written config.