proper support for "isabelle update -D DIR": avoid accidental exclusion of select_dirs (amending e5dafe9e120f);
@inproceedings{MehtaN-CADE03,author={Farhad Mehta and Tobias Nipkow},
title={Proving Pointer Programs in Higher-Order Logic},
booktitle="Automated Deduction --- CADE-19",editor="F. Baader",
year=2003,publisher="Springer",series="LNCS",volume={2741},pages={121--135}}
@article{MehtaN-IC05,author={Farhad Mehta and Tobias Nipkow},
title={Proving Pointer Programs in Higher-Order Logic},
journal="Information and Computation",year=2005,volume=199,pages={200-227}}