tree: fix handling of multi-row stdin input (#54)
This was broken by the GtkColumnView port (7a80b670). As part of the changes that just stopped any attempt to actually start a new row here, so we just kept stuffing more and more items into the only row item we ever create. So you just couldn't do multi- row input via stdin.
Signed-off-by: Adam Williamson awilliam@redhat.com