various - minor spelling, include guard fixes

also clean duplicate includes

Change-Id: I3fdd02fd1d07e7061003dd5fbed9e04b7b9ca928
Reviewed-on: https://codereview.kdab.com/70210
Reviewed-by: Sérgio Martins <sergio@kdab.com>

src/DockWidgetBase.cpp

@@ -30,7 +30,6 @@
 #include "DropArea_p.h"
 #include "LastPosition_p.h"
 #include "multisplitter/Item_p.h"
-#include "DockRegistry_p.h"
 #include "Config.h"
 #include "FrameworkWidgetFactory.h"
 
@@ -226,7 +225,7 @@ void DockWidgetBase::setFloating(bool floats)
             d->restoreToPreviousPosition();
         } else {
             qCDebug(placeholder) << Q_FUNC_INFO << "Don't have a place to restore";
-            // TODO: Restore to prefered place ?
+            // TODO: Restore to preferred place ?
         }
     }
 }