Added EVENT_FLAG_AGI and used it for manager calls in res_agi.c

(closes issue #13873)
Reported by: fnordian
Patches:
      ami_agievent.patch uploaded by fnordian (license 110)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@158876 65c4cc65-6c06-0410-ace0-fbb531ad65f3