Add some test coverage for board moves

Summary: Ref T10010. This isn't totally comprehensive, and a lot of behaviors aren't testable (e.g., all the Javascript stuff) but at least covers the basic create/move/reorder operations.

Test Plan: `arc unit`

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10010

Differential Revision: https://secure.phabricator.com/D15178

src/applications/project/engine/PhabricatorBoardLayoutEngine.php

@@ -23,7 +23,7 @@ final class PhabricatorBoardLayoutEngine extends Phobject {
   }
 
   public function setBoardPHIDs(array $board_phids) {
-    $this->boardPHIDs = $board_phids;
+    $this->boardPHIDs = array_fuse($board_phids);
     return $this;
   }
 
@@ -32,7 +32,7 @@ final class PhabricatorBoardLayoutEngine extends Phobject {
   }
 
   public function setObjectPHIDs(array $object_phids) {
-    $this->objectPHIDs = $object_phids;
+    $this->objectPHIDs = array_fuse($object_phids);
     return $this;
   }