Allow disconnect feature before a call is bridged

Allow disconnect feature before a call is bridged

feature.conf has a disconnect option.  By default this option is set to '*', but it could be anything.  If a user wishes to disconnect a call before the other side answers, only '*' will work, regardless if the disconnect option is set to something else.  This is because features are unavailable until bridging takes place.  The default disconnect option, '*', was hardcoded in app_dial, which doesn't make any sense from a user perspective since they may expect it to be something different.  This patch allows features to be detected from outside of the bridge, but not operated on.  In this case, the disconnect feature can be detected before briding and handled outside of features.c.

(closes issue #11583)
Reported by: sobomax
Patches:
	patch-apps__app_dial.c uploaded by sobomax (license 359)
	11583.latest-patch uploaded by murf (license 17)
	detect_disconnect.diff uploaded by dvossel (license 671)
Tested by: sobomax, dvossel
Review: http://reviewboard.digium.com/r/195/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@183126 65c4cc65-6c06-0410-ace0-fbb531ad65f3