Item11470: Fix linkattachments parameter

Documented as linkattachments, but it was implemented as linkfiles.
Test logic was incorrect, so attachments were always linked regardless
of the requested setting.

git-svn-id: http://svn.foswiki.org/trunk/DirectedGraphPlugin@17193 0b4bb1d4-4e5a-0410-9cc4-b2b747904278