A fair number of changes for the sake of bug 7506

apps/app_voicemail.c

channels/chan_agent.c

channels/chan_alsa.c

channels/chan_features.c

channels/chan_gtalk.c

channels/chan_h323.c

channels/chan_iax2.c

channels/chan_jingle.c

channels/chan_local.c

channels/chan_mgcp.c

channels/chan_misdn.c

channels/chan_nbs.c

channels/chan_oss.c

channels/chan_phone.c

channels/chan_sip.c

channels/chan_skinny.c

channels/chan_vpb.cc

channels/chan_zap.c

include/asterisk/channel.h

include/asterisk/stringfields.h