Don't parse FLTK arguments using Fl::arg; handle -display as other options

Fl::arg accepts several arguments which we are not documenting. Also,
it accepts a -geometry argument, which clashes with our own -geometry
option.
diff --git a/vncviewer/vncviewer.cxx b/vncviewer/vncviewer.cxx
index 426be27..bd3a562 100644
--- a/vncviewer/vncviewer.cxx
+++ b/vncviewer/vncviewer.cxx
@@ -495,9 +495,6 @@
   }
 
   for (int i = 1; i < argc;) {
-    if (Fl::arg(argc, argv, i))
-      continue;
-
     if (Configuration::setParam(argv[i])) {
       i++;
       continue;
@@ -522,6 +519,9 @@
   mkvnchomedir();
 
 #if !defined(WIN32) && !defined(__APPLE__)
+  if (strcmp(display, "") != 0) {
+    Fl::display(display);
+  }
   fl_open_display();
   XkbSetDetectableAutoRepeat(fl_display, True, NULL);
 #endif