QmlJS: Fix infinite loop when scanning for exported C++ types.

Setting extra diagnostics would call updateDocument which would in turn
trigger another scan.

Change-Id: I3810a380cdf716a12767d94ff82dc30f8ae3954d
Reviewed-on: http://codereview.qt.nokia.com/3917
Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>
Reviewed-by: Leandro T. C. Melo <leandro.melo@nokia.com>

src/libs/cplusplus/ModelManagerInterface.h

@@ -154,6 +154,7 @@ public:
 Q_SIGNALS:
     void documentUpdated(CPlusPlus::Document::Ptr doc);
     void sourceFilesRefreshed(const QStringList &files);
+    void extraDiagnosticsUpdated(QString fileName);
 
 public Q_SLOTS:
     virtual void updateModifiedSourceFiles() = 0;