+New)Unify Old with an absolute path to the current working
directory and change working directory to New. Use the
working_directory(CWD, CWD) to get the current directory.
See also absolute_file_name/2
of the file I/O predicates use local filenames. Changing directory while
file-bound streams are open causes wrong results on telling/1, seeing/1
Note that the working directory is shared between all threads.
Applications are strongly encouraged not to change the working directory
or change the working directory once during the initialization.