Added helpful log warning if failure to bind server port (port in use?).

src/sbbs3/ftpsrvr.c

@@ -4323,6 +4323,7 @@ void DLLCALL ftp_server(void* arg)
     	,sizeof(server_addr)))!=0) {
 		lprintf("%04d !ERROR %d (%d) binding socket to port %u"
 			,server_socket, result, ERROR_VALUE,startup->port);
+		lprintf("!Another service may be using this port");
 		cleanup(1);
 		return;
 	}

src/sbbs3/mailsrvr.c

@@ -2482,6 +2482,7 @@ void DLLCALL mail_server(void* arg)
 	if (result != 0) {
 		lprintf("%04d !ERROR %d (%d) binding SMTP socket to port %u"
 			,server_socket, result, ERROR_VALUE, startup->smtp_port);
+		lprintf("!Another service may be using this port");
 		cleanup(1);
 		return;
 	}
@@ -2527,6 +2528,7 @@ void DLLCALL mail_server(void* arg)
 		if (result != 0) {
 			lprintf("%04d !ERROR %d (%d) binding POP3 socket to port %u"
 				,pop3_socket, result, ERROR_VALUE, startup->pop3_port);
+			lprintf("!Another service may be using this port");
 			cleanup(1);
 			return;
 		}

src/sbbs3/main.cpp

@@ -3152,6 +3152,7 @@ void DLLCALL bbs_thread(void* arg)
 	if(result != 0) {
 		lprintf("!ERROR %d (%d) binding Telnet socket to port %d"
 			,result, ERROR_VALUE,startup->telnet_port);
+		lprintf("!Another service may be using this port");
 		cleanup(1);
 		return;
 	}
@@ -3208,6 +3209,7 @@ void DLLCALL bbs_thread(void* arg)
 		if(result != 0) {
 			lprintf("!ERROR %d (%d) binding RLogin socket to port %d"
 				,result, ERROR_VALUE,startup->rlogin_port);
+			lprintf("!Another service may be using this port");
 			cleanup(1);
 			return;
 		}