Do not scan "/" for include files

The scanning phase was in some cases insanely long.
Reason was that Creator feeds wrong paths to the
CppModelManager, for example "/".

The scanning phase did what it was told to: scan that whole
Harddrive.

This patch makes sure that the scanning is not done for "/"

Done-With: Roberto

src/plugins/cpptools/cppmodelmanager.cpp

@@ -1231,6 +1231,9 @@ void CppModelManager::updateIncludesInPaths(QFutureInterface<void> &future,
 
         const QString path = paths.takeFirst();
 
+        if (path == QLatin1String("/"))
+            continue;
+
         // Skip non-existing paths
         if (!QFile::exists(path))
             continue;