MBS-6449: Enable guess_search on per-entity edit listings
MBS-6449: Only say 'at least n edits' if n >= 500

As the extended comment in root/edit/list.tt mentions:

  If we have less than 500 entries then we know we don't have an
  estimate (because 500 is only the upper bound), so we only
  indicate the search is an estimate if we have more than >= 500
  total results.

MBS-6449 has the example of a search that returns exactly 100
edits. 100 % 50 == 0 && last_page > 1 is true, so previously the
code would think this search was just a guess. However, we know
100 < 500, the limit, so we know that this can't be a guess.
Merge branch 'mbs-6798' into beta