Get rid of _once(); inlining it takes less code. :-)

Get rid of _once(); inlining it takes less code. :-)

Also, don't call gettempdir() in the default expression for the 'dir'
argument to various functions; use 'dir=None' for the default and
insert 'if dir is None: dir = gettemptir()' in the bodies.  That way
the work done by gettempdir is postponed until needed.