use a different method for overriding the send_digit_begin pointer, as the old...

use a different method for overriding the send_digit_begin pointer, as the old one fails to compile on my 64-bit system with gcc-4.1 and --enable-dev-mode turned on


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@77820 65c4cc65-6c06-0410-ace0-fbb531ad65f3