The calendaring tech modules depend on res_calendar and initially
res_calendar just bumped the use count so that it couldn't be unloaded.
res_calendar can potentially create many threads and I've seen issues
where the Asterisk shutdown has failed where it looked like these
threads could be the culprit.
This patch adds unload support for res_calendar. Unloading res_calendar
will also unload the dependant tech modules as well.
(closes issue ASTERISK-16744)
Review: https://reviewboard.asterisk.org/r/1657/
git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@353502 65c4cc65-6c06-0410-ace0-fbb531ad65f3