Display.c: add a describing comment for nxagentDisplayErrorPredicate

nx-X11/programs/Xserver/hw/nxagent/Display.c

@@ -754,6 +754,20 @@ static void nxagentDisplayFlushHandler(Display *display, int length)
   }
 }
 
+/*
+ * From the changelog for nx-X11-3.0.0-4:
+ * "Added the _NXDisplayErrorPredicate function in XlibInt.c. It is
+ * actually a pointer to a function called whenever Xlib is going to
+ * perform a network operation. If the function returns true, the
+ * call will be aborted and Xlib will return the control to the ap-
+ * plication. It is up to the application to set the XlibDisplayIO-
+ * Error flag after the _NXDisplayErrorPredicate returns true. The
+ * function can be used to activate additional checks, besides the
+ * normal failures detected by Xlib on the display socket. For exam-
+ * ple, the application can set the funciton to verify if an inter-
+ * rupt was received or if any other event occurred mandating the
+ + end of the session."
+ */
 static int nxagentDisplayErrorPredicate(Display *display, int error)
 {
   #ifdef TEST