Qt4ProjectManager: Do not enumerate files from cumulatively found folders

Ignore folders from cumulative parse, we are recursively enumerating all the
files from those folders and add watchers for them, that's too dangerous
if we get the foldrs wrong and enumerate the whole project tree multiple
times.

Task-Nr: QTCREATORBUG-3104

Reviewed-By: con
Reviewed-By: Alessandro Portale