A number of bug fixes to mrouted (no functionality enhancements from 3.5, just
the fixes!):

o Scoped addresses might let traffic in
o IGMP queries sent with wrong timeouts
o Possible core dump in mtrace if we get a request for which we have no route
o If a member on a transit network left a group, mrouted would stop forwarding

even if there was a downstream router

o Various code cleanups and logging changes

Reviewed by: wollman
Submitted by: Bill Fenner <fenner@parc.xerox.com>