tests/test-gendoc-it.t

vfs: use 'vfs' module directly in 'mercurial.unionrepo'

Now that the 'vfs' classes moved in their own module, lets use the new module
directly. We update code iteratively to help with possible bisect needs in the
future.

#require docutils gettext

  $ $TESTDIR/check-gendoc it
  checking for parse errors