Fix table definition parsing as unprivileged user

revision 1.689 introduced warn_duplicate_tables() unconditionally, breaking
the parser on tables withs insufficient permissions to open pf(4):

	$ echo 'table <t>' | pfctl -nf-
	pfctl: pfr_get_tables: Bad file descriptor

So simply check whether pfctl is able to get the table list first.  If not,
instead of silently avoiding namespace collision checks, print a brief
notice iff `-v' is given to help finding duplicate definitions by hand:

	$ echo 'table <t>' | ./obj/pfctl -vnf-
	table <t>
	stdin:1: skipping duplicate table checks for <t>

Reported by Rivo Nurges, thanks!
OK benno sashan

0 files changed, 0 insertions, 0 deletions