merge markster's usersconf branch with some slight changes

apps/app_directory.c

apps/app_voicemail.c

channels/chan_iax2.c

channels/chan_sip.c

channels/chan_zap.c

configs/extensions.conf.sample

configs/users.conf.sample

configs/voicemail.conf.sample

include/asterisk/config.h

include/asterisk/pbx.h

main/asterisk.c

main/config.c

main/manager.c

main/pbx.c

pbx/pbx_config.c