Prevent duplicated project entries on failed project loading

Change-Id: I4505d0957398d47c40843dbcbf8ce25365f6501d
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>

src/plugins/projectexplorer/session.cpp

@@ -313,7 +313,10 @@ bool SessionManager::save()
         projectFiles << pro->document()->fileName();
 
     // Restore infromation on projects that failed to load:
-    projectFiles.append(m_failedProjects);
+    // don't readd projects to the list, which the user loaded
+    foreach (const QString &failed, m_failedProjects)
+        if (!projectFiles.contains(failed))
+            projectFiles << failed;
 
     writer.saveValue(QLatin1String("ProjectList"), projectFiles);