tasks #6774 Stack values when having same label multiple times

Change-Id: I94f7ca48cacf3d3e7e435822e75cd301d741384d
Merge commit 'refs/changes/65/2365/1' of ssh://gerrit.tuleap.net:29418/tuleap into tuleap-stable-master

* ssh://gerrit.tuleap.net:29418/tuleap:
  tasks #6774 Stack values when having same label multiple times

Change-Id: I0a9a325005546aadddef70ea413c91704e885c79
Tuleap 6.12.99.99

Change-Id: Id007cf15f9ae7f4f003effa675804c95e982650c