Computing the roots in a set of tasks is generally useful.  Refs #9648.
Computing the roots in a set of tasks is generally useful.  Refs #9648.

Note that if no parent field is configured, all tickets are roots.

git-svn-id: 2159781fc7c14c6bdd1f7e265daf7a25099c31e7@11425 7322e99d-02ea-0310-aa39-e9a107903beb

trac-hacks/trac-jsGantt,trac-hacks/trac-jsGantt,trac-hacks/trac-jsGantt