Vacuum crufty leaf pages.

There may be pages that do not get rewritten but have a lot of appends. A page may have a record that is inserted and deleted repeatedly, without ever reaching a point where the page will split. I'm considering adding a journal entry number to the appended record, so we'll know how many entries are in the leaf page. A rewritten journal will have one extra entry for the number of records in the page, or two if we take to writing a position array record at the head of the file.