Refactoring changes: Cleanup and improvements.

Previously RefactoringFiles were usually passed around by value.
However, since a RefactoringFile may sometimes own a QTextDocument
(when it was read from a file), that's not great and caused the
file to be reread after every copy.

With this change RefactoringFile becomes noncopyable and is always
owned by a shared pointer.

This change also allowed having const RefactoringFiles which is
useful because they can be safely used from other threads. See
CppRefactoringChanges::fileNoEditor.

Change-Id: I9045921d6d0f6349f9558ff2a3d8317ea172193b
Reviewed-on: http://codereview.qt.nokia.com/3084
Reviewed-by: Leandro T. C. Melo <leandro.melo@nokia.com>

src/plugins/qmljseditor/qmljsquickfixassist.h

@@ -51,12 +51,13 @@ public:
     virtual ~QmlJSQuickFixAssistInterface();
 
     const SemanticInfo &semanticInfo() const;
-    const QmlJSTools::QmlJSRefactoringFile currentFile() const;
+    QmlJSTools::QmlJSRefactoringFilePtr currentFile() const;
     QWidget *widget() const;
 
 private:
     QmlJSTextEditorWidget *m_editor;
     SemanticInfo m_semanticInfo;
+    QmlJSTools::QmlJSRefactoringFilePtr m_currentFile;
 };