Squash collection shares

If folder1 is shared to user2 and user3. And folder1/folder2 is shared
to user4 and user5 then getting all the users with access to
folder1/folder2 should only list user2 and user 3 once.

Previously this was done twice since we request the info two times.

This fix makes sure that we only append unique results to the array.

* Added test