schemas/util.sql: added show_types_like()

bugfix: schemas/util.sql: functions marked IMMUTABLE: changed to STABLE or VOLATILE where IMMUTABLE would cause preemptive inlining (http://vegpath.org/links/#PostgreSQL:%20Documentation:%209.3:%20Function%20Volatility%20Categories%20**)

bugfix: schemas/util.sql: functions marked IMMUTABLE: changed to STABLE or VOLATILE where IMMUTABLE would cause preemptive inlining (http://vegpath.org/links/#PostgreSQL:%20Documentation:%209.3:%20Function%20Volatility%20Categories%20**)

schemas/vegbien.sql: locationevent: documented `UPDATE locationevent SET place_visit_id = place_visit_id` runtime (>~1 h)

schemas/util.sql: added relation_type(regtype) so drop_relation() would work on TYPEs, too. TYPEs are sometimes used as a function return type linked to a particular table (eg. in the keys() functions), and should be dropped along with the table by util.drop_relations_like().

schemas/util.sql: drop_relation(regclass): support any type that has a util.relation_type()

fix: schemas/vegbien.sql: _plots_10_count_of_individuals_per_plot_in_each_project: fixed to handle subplots properly, using new locationevent.place_visit_id

schemas/vegbien.sql: added place_visit view, analogous to plot but for top-level locationevents. this is needed by the SALVIAS validation queries.

schemas/vegbien.sql: locationevent: added locationevent_set_place_visit_id() trigger, analogous to location_set_plot_location_id() but for the locationevent nesting hierarchy. this is needed by the SALVIAS validation queries.

fix: schemas/vegbien.sql: location_set_plot_location_id(): removed incorrect comment that this is a pull-forward trigger