when reading .ext files with "equiv" statements in them. The
generation of "equiv" statements was expanded recently, making it
more likely for this issue to show up. There may be devices in
a file that have a terminal node pointing to the node that gets
removed, and these must be updated to point to the node that
remains after merging. This requires a full loop over all
devices and so could have a potentially large impact; but in
general there are not many equiv statements (implying multiple
different labels attached to the same node) and so it is unlikely
that there would be a noticeable performance hit in practice.
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