chan_local+app_dial: Propagagate call answered elsewhere over local channels.

AST_FLAG_ANSWERED_ELSEWHERE was not propagated back from local channels.
It is now. That means that when a call is picked up from a callgroup of
local channels, the other channels will now properly see it as "picked up".

This occurs when you use a construct like Dial(Local/a@context&Local/b@context)
where a@context and b@context dial two chan_sip devices respectively. If one
device picks up, the other will not see "1 missed call" anymore. In this
respect, it now behaves the same as when doing Dial(SIP/a&SIP/b).

Review: https://reviewboard.asterisk.org/r/3540/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@413949 f38db490-d61c-443f-a65b-d21fe96a405b