[optional] Javascript-enabled +/- controls that allow branches in the dependency tree to collapse. Patch by Mike Shaver <shaver@mozilla.org>, minor cleanups by me, r=myk, kiko, a=justdave. git-svn-id: svn://10.0.0.236/trunk@154045 18797224-902f-48f8-a5cc-f745e15eee43