schemas/util.sql: added mk_set_relation_metadata()

bugfix: inputs/.TNRS/schema.sql: map_taxonomic_status(): need to use accepted name instead of scrubbed name (which also includes no-opinion names), as described at http://wiki.vegpath.org/2013-11-14_conference_call#taxonomic-fields. this used to be the accepted name, but got switched when the concatenated name was also used to store the matched name for no-opinion names.

schemas/public_.sql: _plots_20_tnrs_names: use accepted_morphospecies_binomial, which is now available directly in the TNRS results, instead of just the morphospecies_suffix, as requested in issue #915

inputs/.TNRS/schema.sql: MatchedTaxon: documented how to modify it (using util.force_recreate())

schemas/util.sql: force_recreate(): documented usage, which is somewhat complex and has several important parts

inputs/.TNRS/schema.sql: MatchedTaxon, etc.: added accepted_morphospecies_binomial derived field

bugfix: schemas/util.sql: restore_views(): need to specify view name for a manual existence check, in case the view definition becomes invalid, which would produce a nonstandard (uncatchable) exception

bugfix: schemas/util.sql: explain(): don't display any log messages printed by IMMUTABLE functions in the query, which EXPLAIN apparently runs

schemas/util.sql: create_if_not_exists(): added relation param, which can be used to ensure that a standard exception is always generated if the relation exists, even if the table definition would be invalid (which generates a variety of exceptions)

bugfix: schemas/util.sql: try_cast(), is_castable(): also need to handle syntax_error_or_access_rule_violation, which is thrown by ::regclass