CppTools: Check if project has changed before reparsing

This introduces an API change for the project managers. Those are not
expected to call updateSourceFiles() anymore.

Task-number: QTCREATORBUG-9581
Change-Id: I77befd29fb851c9acf87204d571da00183c9cd05
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/cpptools/cpptoolsplugin.h

@@ -163,6 +163,7 @@ private slots:
     void test_modelmanager_framework_headers();
     void test_modelmanager_refresh_also_includes_of_project_files();
     void test_modelmanager_refresh_several_times();
+    void test_modelmanager_refresh_test_for_changes();
     void test_modelmanager_snapshot_after_two_projects();
     void test_modelmanager_extraeditorsupport_uiFiles();