Be willing to follow a symlink if the user specifies one as the root

Be willing to follow a symlink if the user specifies one as the root
of the recursive scan, on the grounds that they're more likely to
have wanted a scan of the link target than of the link itself. We
still don't follow symlinks once we've started recursing, of course.

git-svn-id: svn://svn.tartarus.org/sgt/agedu@8329 cda61777-01e9-0310-a592-d414129be87e