Handle milestone dates better.  Refs #8959.
Handle milestone dates better.  Refs #8959.

No longer assume that milestone dates are microseconds.  Use Trac API
to do version-indenpendent conversion.

Patch thanks to rjollos.

git-svn-id: 2159781fc7c14c6bdd1f7e265daf7a25099c31e7@10407 7322e99d-02ea-0310-aa39-e9a107903beb

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