Move the plugin examples to subdir of pluginhowto.

doc/pluginhowto/examples/preferencepane/preferencepaneplugin.cpp

@@ -0,0 +1,36 @@
+#include "preferencepaneplugin.h"
+#include "modifiedfilelister.h"
+
+#include <QtPlugin>
+#include <QStringList>
+
+PreferencePanePlugin::PreferencePanePlugin()
+{
+    // Do nothing
+}
+
+PreferencePanePlugin::~PreferencePanePlugin()
+{
+    // Do notning
+}
+
+void PreferencePanePlugin::extensionsInitialized()
+{
+    // Do nothing
+}
+
+bool PreferencePanePlugin::initialize(const QStringList& args, QString *errMsg)
+{
+    Q_UNUSED(args);
+    Q_UNUSED(errMsg);
+
+    addAutoReleasedObject(new ModifiedFileLister);
+    return true;
+}
+
+void PreferencePanePlugin::shutdown()
+{
+    // Do nothing
+}
+
+Q_EXPORT_PLUGIN(PreferencePanePlugin)