Refactor assignment of start and finish dates.
Refactor assignment of start and finish dates.

This is ground work for refining the scheduling algorithm.

_Real_ scheduling would require doing this from the end (tickets
without sucessors) back to the beginning along a chain of dependent
tasks.  For now we just set dates based on milestones so we just
"schedule" each ticket independently.


git-svn-id: 2159781fc7c14c6bdd1f7e265daf7a25099c31e7@10036 7322e99d-02ea-0310-aa39-e9a107903beb

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