attic extension broken by updatedir move in hg 1.7+

[John Hein]

updatedir() was moved from patch.py to cmdutils.py.  It was called by the attic extension, so that is now broken when using mercurial 1.7.

It's easy enough to call cmdutils.updatedir instead of patch.updatedir, but that means it will break if used with hg 1.6 or earlier.  What's the right way for 3rd party extensions to be portable across different mercurial versions?