Move IEditor::isTemporary to IDocument

It's a property of the document implementation, not of the specific
editor instance working on it.

Change-Id: I5c3dd054e21b646e2d94b891916a096d045923f8
Reviewed-by: hjk <hjk121@nokiamail.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/diffeditor/diffeditor.h

@@ -64,7 +64,6 @@ public:
     bool open(QString *errorString, const QString &fileName, const QString &realFileName);
     Core::IDocument *document();
     Core::Id id() const;
-    bool isTemporary() const { return true; }
     DiffEditorWidget *editorWidget() const { return m_editorWidget; }
 
     QWidget *toolBar();

src/plugins/diffeditor/diffeditorfile.cpp

@@ -43,6 +43,7 @@ DiffEditorFile::DiffEditorFile(const QString &mimeType, QObject *parent) :
     m_modified(false)
 {
     setDisplayName(QCoreApplication::translate("DiffEditor", Constants::DIFF_EDITOR_DISPLAY_NAME));
+    setTemporary(true);
 }
 
 void DiffEditorFile::setModified(bool modified)

src/plugins/diffeditor/diffeditorwidget.cpp

@@ -113,7 +113,6 @@ public:
     }
 
     Core::Id id() const { return "DiffViewEditor"; }
-    bool isTemporary() const { return false; }
 
 private slots:
     void slotTooltipRequested(TextEditor::ITextEditor *editor, const QPoint &globalPoint, int position);

src/plugins/diffeditor/diffshoweditor.cpp

@@ -54,7 +54,6 @@ public:
     DiffShowEditorWidgetEditable(BaseTextEditorWidget *editorWidget) : BaseTextEditor(editorWidget) {}
 
     Core::Id id() const { return "DiffShowViewEditor"; }
-    bool isTemporary() const { return false; }
 };
 
 class DiffShowEditorWidget : public BaseTextEditorWidget