request #6594: no more able to sort on a computed field

Change-Id: Ifd67bb053ee6f56e8358f20ece1569ac15ac0e80
Merge commit 'refs/changes/22/2222/3' of ssh://gerrit.tuleap.net:29418/tuleap into stable

* ssh://gerrit.tuleap.net:29418/tuleap:
  request #6594: no more able to sort on a computed field
This is Tuleap 6.12.99.7

Change-Id: Ie0378092622c5a04bc04701ebd68d2bce09e8bc0