Restore the 'w' modifier support for ISDN spans. Dial(DAHDI/g0/1234w888)

Restore the 'w' modifier support for ISDN spans.  Dial(DAHDI/g0/1234w888)

This feature also causes the sending complete ie to be sent for switch
types that do not automatically send the ie.  (EuroISDN/ETSI)

The main difference between dialing Dial(DAHDI/g0/1234w888) and
Dial(DAHDI/g0/1234,,D(888)) is the sending of the sending complete ie.

(closes issue ASTERISK-19176)
Reported by: rmudgett
Tested by: rmudgett
........

Merged revisions 353867 from http://svn.asterisk.org/svn/asterisk/branches/1.8

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/10@353868 65c4cc65-6c06-0410-ace0-fbb531ad65f3