Fix a bug in bsd.port.mk that was causing 'make clean' to fail in some

Fix a bug in bsd.port.mk that was causing 'make clean' to fail in some
ports directories with mysterious symptoms like 'cd: can't cd to &&'.

The problem was that the text of the DragonFly port override warning
message was mistakenly being injected into the output of the
'*-depends-list' targets.  Although the message was being explicitly
filtered out if the target was 'all-depends-list', the targets
'build-depends-list' and 'run-depends-list', exercised indirectly by
'make clean', still allowed it to slip through.

Encountered-by: walt <wa1ter@myrealbox.com> and others
Detective-work-by: walt <wa1ter@myrealbox.com>
Patch-written-by: cpressey
Approved-by: dillon