Inline comment selection is duplicated when the imported page has several revisions

If a user has commented on a text reading "GIVEN" and the page has since had 3 revisions, the selection field in the imported comment object will read something like "GIVENGIVENGIVENGIVEN".

This is because we forgot to reset the inline comment storage between page revisions. At parse time, the selected text is therefore incorrectly added to the existing parsed selection.