Because chdir/getcwd is global to the whole process, it is not thread-safe
and may cause very serious bugs like data loss (for example when 'os.remove'
or 'shutil.rmtree' are called with relative paths).

There still remain uses of 'chdir' in ERP5 Subversion. A temporary quick change
is done to reduce the probability of race conditions, but this should really be
fixed.