Handle -displayfd and an explicit display number sensibly

nx-X11/programs/Xserver/dix/globals.c

@@ -149,7 +149,8 @@ int defaultColorVisualClass = -1;
 int monitorResolution = 0;
 
 char *display;
-int displayfd;
+int displayfd = -1;
+Bool explicit_display = FALSE;
 
 CARD32 TimeOutValue = DEFAULT_TIMEOUT * MILLI_PER_SECOND;
 int	argcGlobal;

nx-X11/programs/Xserver/include/opaque.h

@@ -53,6 +53,7 @@ extern int argcGlobal;
 extern char **argvGlobal;
 extern char *display;
 extern int displayfd;
+extern Bool explicit_display;
 
 extern int defaultBackingStore;
 extern Bool disableBackingStore;

nx-X11/programs/Xserver/os/connection.c

@@ -361,8 +361,8 @@ void
 NotifyParentProcess(void)
 {
 #if !defined(WIN32)
-    if (dynamic_display[0]) {
-        write(displayfd, dynamic_display, strlen(dynamic_display));
+    if (displayfd >= 0) {
+        write(displayfd, display, strlen(display));
         close(displayfd);
     }
     if (RunFromSmartParent) {
@@ -410,18 +410,17 @@ CreateWellKnownSockets(void)
     FD_ZERO (&WellKnownConnections);
 
     /* display is initialized to "0" by main(). It is then set to the display
-     * number if specified on the command line, or to NULL when the -displayfd
-     * option is used. */
+     * number if specified on the command line. */
     if (NoListenAll) {
 	ListenTransCount = 0;
     }
-    else if (display) {
+    else if ((displayfd < 0) || explicit_display) {
         if (TryCreateSocket(atoi(display), &partial) &&
             ListenTransCount >= 1)
             if (!PartialNetwork && partial)
                 FatalError ("Failed to establish all listening sockets");
     }
-    else { /* -displayfd */
+    else { /* -displayfd and no explicit display number */
 	Bool found = 0;
 	for (i = 0; i < 65535 - X_TCP_PORT; i++) {
 	    if (TryCreateSocket(i, &partial) && !partial) {

nx-X11/programs/Xserver/os/utils.c

@@ -704,6 +704,7 @@ ProcessCommandLine(int argc, char *argv[])
 	{
 	    /* initialize display */
 	    display = argv[i];
+	    explicit_display = TRUE;
 	    display++;
             if( ! VerifyDisplayName( display ) ) {
                 ErrorF("Bad display name: %s\n", display);
@@ -783,7 +784,6 @@ ProcessCommandLine(int argc, char *argv[])
 	else if (strcmp(argv[i], "-displayfd") == 0) {
 	    if (++i < argc) {
 		displayfd = atoi(argv[i]);
-		display = NULL;
 		nolock = TRUE;
 	    }
 	    else