use_dir and exit_use_dir now change the CWD only temporarily
use_dir and exit_use_dir now change the CWD only temporarily

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle