allow enter and exit sounds to interrupt the MOH in a wait_mod conference

This patch does the following:
* only starts MOH if no other file (sync or async) is currently playing
* adds a variable "conference_permanent_wait_mod_moh" that controls the
  behavior of how the enter and exit sounds interact with the MOH when
  wait_mod is set. When the variable is set, the MOH keeps playing and
  the enter and exit sounds are mixed with the MOH. When the variable
  is unset, then any playing MOH is first stopped, then the enter or
  exit sound is played and the MOH is started again.

This functionality is useful in case the enter and exit sounds are
used to announce the name of the caller, who is joining or leaving a
conference.

FS-5159 #resolve

src/mod/applications/mod_conference/mod_conference.c

@@ -2277,7 +2277,8 @@ static switch_status_t conference_add_member(conference_obj_t *conference, confe
 		}
 
 		if (conference->count > 1) {
-			if (conference->moh_sound && !switch_test_flag(conference, CFLAG_WAIT_MOD)) {
+			if ((conference->moh_sound && !switch_test_flag(conference, CFLAG_WAIT_MOD)) ||
+					(switch_test_flag(conference, CFLAG_WAIT_MOD) && !switch_true(switch_channel_get_variable(channel, "conference_permanent_wait_mod_moh")))) {
 				/* stop MoH if any */
 				conference_stop_file(conference, FILE_STOP_ASYNC);
 			}
@@ -2287,10 +2288,9 @@ static switch_status_t conference_add_member(conference_obj_t *conference, confe
 				if (switch_test_flag(conference, CFLAG_ENTER_SOUND)) {
 					if (!zstr(enter_sound)) {
 				     	conference_play_file(conference, (char *)enter_sound, CONF_DEFAULT_LEADIN,
-						     	switch_core_session_get_channel(member->session), !switch_test_flag(conference, CFLAG_WAIT_MOD) ? 0 : 1);
+							switch_core_session_get_channel(member->session), 0);
 			        } else {	
-				     		conference_play_file(conference, conference->enter_sound, CONF_DEFAULT_LEADIN, switch_core_session_get_channel(member->session),
-								!switch_test_flag(conference, CFLAG_WAIT_MOD) ? 0 : 1);
+						conference_play_file(conference, conference->enter_sound, CONF_DEFAULT_LEADIN, switch_core_session_get_channel(member->session), 0);
 					}
 				}
 			}
@@ -2316,7 +2316,7 @@ static switch_status_t conference_add_member(conference_obj_t *conference, confe
 						if (conference->alone_sound  && !switch_test_flag(member, MFLAG_GHOST)) {
 							conference_stop_file(conference, FILE_STOP_ASYNC);
 							conference_play_file(conference, conference->alone_sound, CONF_DEFAULT_LEADIN,
-												 switch_core_session_get_channel(member->session), 1);
+												 switch_core_session_get_channel(member->session), 0);
 						} else {
 							switch_snprintf(msg, sizeof(msg), "You are currently the only person in this conference.");
 							conference_member_say(member, msg, CONF_DEFAULT_LEADIN);
@@ -2683,7 +2683,7 @@ static switch_status_t conference_del_member(conference_obj_t *conference, confe
 
 	if (member->session && (exit_sound = switch_channel_get_variable(switch_core_session_get_channel(member->session), "conference_exit_sound"))) {
 		conference_play_file(conference, (char *)exit_sound, CONF_DEFAULT_LEADIN,
-							 switch_core_session_get_channel(member->session), !switch_test_flag(conference, CFLAG_WAIT_MOD) ? 0 : 1);
+							 switch_core_session_get_channel(member->session), 0);
 	}
 
 
@@ -2786,12 +2786,16 @@ static switch_status_t conference_del_member(conference_obj_t *conference, confe
 			|| (switch_test_flag(conference, CFLAG_DYNAMIC) && (conference->count + conference->count_ghosts == 0))) {
 			switch_set_flag(conference, CFLAG_DESTRUCT);
 		} else {
+			if (!switch_true(switch_channel_get_variable(channel, "conference_permanent_wait_mod_moh")) && switch_test_flag(conference, CFLAG_WAIT_MOD)) {
+				/* Stop MOH if any */
+				conference_stop_file(conference, FILE_STOP_ASYNC);
+			}
 			if (!exit_sound && conference->exit_sound && switch_test_flag(conference, CFLAG_EXIT_SOUND)) {
 				conference_play_file(conference, conference->exit_sound, 0, channel, 0);
 			}
 			if (conference->count == 1 && conference->alone_sound && !switch_test_flag(conference, CFLAG_WAIT_MOD) && !switch_test_flag(member, MFLAG_GHOST)) {
 				conference_stop_file(conference, FILE_STOP_ASYNC);
-				conference_play_file(conference, conference->alone_sound, 0, channel, 1);
+				conference_play_file(conference, conference->alone_sound, 0, channel, 0);
 			}
 		}
 
@@ -3146,7 +3150,7 @@ static void *SWITCH_THREAD_FUNC conference_thread_run(switch_thread_t *thread, v
 		if (conference->perpetual_sound && !conference->async_fnode) {
 			conference_play_file(conference, conference->perpetual_sound, CONF_DEFAULT_LEADIN, NULL, 1);
 		} else if (conference->moh_sound && ((nomoh == 0 && conference->count == 1) 
-											 || switch_test_flag(conference, CFLAG_WAIT_MOD)) && !conference->async_fnode) {
+									 || switch_test_flag(conference, CFLAG_WAIT_MOD)) && !conference->async_fnode && !conference->fnode) {
 			conference_play_file(conference, conference->moh_sound, CONF_DEFAULT_LEADIN, NULL, 1);
 		}