*fixed segfault at start-up due to faulty allocation of the string length for...

*fixed segfault at start-up due to faulty allocation of the string length for checking for unique instance of pd-l2ork
*made unique check in pd.tk more robust in respect to relative paths and multiple files by making sure that the script always goes back to the original directory from which it was invoked, so as to ensure that the path (if relative) is valid