OPAC Browse: use superpage concept for performance; fix other counting bug

OPAC Browse: use  superpage concept for performance; fix other counting bug

This commit does two totally different things.

1) It implements a superpages concept in the visibility testing that
happens for records linked to displayed browse headings. By default now
we will only test 100 records at at time for visible holdings w/in the
browse scope until at least 1 visible record is found (or the set of
records is exhausted).

In practical terms this will result in display of headings followed by
"at least 100" or "at least 92" instead of larger numbers, but there
should be a big speed win. Yes it's possible, though very unlikely, that
you'd get cases of "at least 1".

When there's less than a browse superpage worth of records to check
anyway, the count should be exact and won't say "at least."

2) It fixes a bug where the counts for the number of bib records linked
to an authority reference heading were not cached properly on the server
side, so upon page reloads or back/forward operations those counts could
disappear.

Signed-off-by: Lebbeous Fogle-Weekley <lebbeous@esilibrary.com>