Comment 8 for bug 192859

TestKindChanges in the attached branch reproduces one of these cases:

<class 'testtools.testresult.real._StringException'>: Text attachment: traceback
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Traceback (most recent call last):
  File "/home/mbp/bzr/192859-2.0-symlinks/bzrlib/tests/per_workingtree/test_symlinks.py", line 84, in test_symlink_to_dir
    tree.smart_add(['tree/a/f'])
  File "/home/mbp/bzr/192859-2.0-symlinks/bzrlib/mutabletree.py", line 53, in tree_write_locked
    return unbound(self, *args, **kwargs)
  File "/home/mbp/bzr/192859-2.0-symlinks/bzrlib/mutabletree.py", line 417, in smart_add
    added.extend(_add_one_and_parent(self, inv, None, rf, kind, action))
  File "/home/mbp/bzr/192859-2.0-symlinks/bzrlib/mutabletree.py", line 671, in _add_one_and_parent
    _add_one(tree, inv, parent_ie, path, kind, action)
  File "/home/mbp/bzr/192859-2.0-symlinks/bzrlib/mutabletree.py", line 688, in _add_one
    inv.add(entry)
  File "/home/mbp/bzr/192859-2.0-symlinks/bzrlib/inventory.py", line 1300, in add
    if entry.name in parent.children:
AttributeError: children
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