Make browse pivot DB funcs STABLE

Since these are just convenience functions doing only selects, these
should be STABLE safe, and making this change allows browse to be
functional on production-size data sets.

Signed-off-by: Dan Wells <dbw2@calvin.edu>
Signed-off-by: Chris Sharp <csharp@georgialibraries.org>
Signed-off-by: Jason Stephenson <jstephenson@mvlc.org>
Stamping upgrade script for 0845: browse pivots should be stable.

Signed-off-by: Jason Stephenson <jstephenson@mvlc.org>