Move IEditor::createNew to IDocument::setContents

The method is for setting the contents, so it belongs to the document,
and should be named correspondingly.

Change-Id: I40363dc08f11268f530885b512e4a88e8b10d096
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/diffeditor/diffshoweditor.h

@@ -42,10 +42,6 @@ QT_END_NAMESPACE
 
 namespace DiffEditor {
 
-namespace Internal {
-class DiffEditorFile;
-}
-
 class DIFFEDITOR_EXPORT DiffShowEditor : public DiffEditor
 {
     Q_OBJECT