Support --option in addition to -option for all builtin Qt commandline options.

In addition to being more common and consistent with QCommandLineParser, this
will make it possible to add the documentation for these options
in the QCommandLineParser-generated help output.

[ChangeLog][General] Builtin command-line options such as -reverse,
-session, -style etc. now all support double dash, e.g. --reverse,
--session, --style...

Change-Id: Ia2e22c854ccc6a9d7b863b1234317005bc822191
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/corelib/kernel/qcoreapplication.cpp

@@ -186,6 +186,8 @@ void QCoreApplicationPrivate::processCommandLineArguments()
             continue;
         }
         QByteArray arg = argv[i];
+        if (arg.startsWith("--"))
+            arg.remove(0, 1);
         if (arg.startsWith("-qmljsdebugger=")) {
             qmljs_debug_arguments = QString::fromLocal8Bit(arg.right(arg.length() - 15));
         } else if (arg == "-qmljsdebugger" && i < argc - 1) {

src/gui/kernel/qguiapplication.cpp

@@ -1018,6 +1018,8 @@ void QGuiApplicationPrivate::createPlatformIntegration()
             continue;
         }
         QByteArray arg = argv[i];
+        if (arg.startsWith("--"))
+            arg.remove(0, 1);
         if (arg == "-platformpluginpath") {
             if (++i < argc)
                 platformPluginPath = QLatin1String(argv[i]);
@@ -1098,6 +1100,8 @@ void QGuiApplicationPrivate::init()
             continue;
         }
         QByteArray arg = argv[i];
+        if (arg.startsWith("--"))
+            arg.remove(0, 1);
         if (arg == "-plugin") {
             if (++i < argc)
                 pluginList << argv[i];

src/plugins/platforms/xcb/qxcbintegration.cpp

@@ -145,18 +145,15 @@ QXcbIntegration::QXcbIntegration(const QStringList &parameters, int &argc, char
     if (argc) {
         int j = 1;
         for (int i = 1; i < argc; i++) {
-            char *arg = argv[i];
-            if (arg) {
-                if (!strcmp(arg, "-display") && i < argc - 1) {
-                    displayName = argv[++i];
-                    arg = 0;
-                } else if (!strcmp(arg, "-name") && i < argc - 1) {
-                    m_instanceName = argv[++i];
-                    arg = 0;
-                }
-            }
-            if (arg)
-                argv[j++] = arg;
+            QByteArray arg(argv[i]);
+            if (arg.startsWith("--"))
+                arg.remove(0, 1);
+            if (arg == "-display" && i < argc - 1)
+                displayName = argv[++i];
+            else if (arg == "-name" && i < argc - 1)
+                m_instanceName = argv[++i];
+            else
+                argv[j++] = argv[i];
         }
         argc = j;
     } // argc

src/widgets/kernel/qapplication.cpp

@@ -446,7 +446,8 @@ void QApplicationPrivate::process_cmdline()
             continue;
         }
         QByteArray arg = argv[i];
-        arg = arg;
+        if (arg.startsWith("--"))
+            arg.remove(0, 1);
         QString s;
         if (arg == "-qdevel" || arg == "-qdebug") {
             // obsolete argument