Use pfctl_fopen (which checks to ensure the given file isn't a directory)

Use pfctl_fopen (which checks to ensure the given file isn't a directory)
for pfctl -f /path/to/pf.conf. Otherwise, if you accidentally use a dir
instead of a file (e.g. if you have an /etc/pf directory and don't notice
the name when tab-completing), you successfully install an empty ruleset.
ok sashan@