bugfix: schemas/vegbien.sql: source_by_shortname(): added schema_anchor so that it always applies to the schema it's defined in, even if `public` is not in the search_path

schemas/vegbien.sql: functions with schema_anchors: documented that they must use LANGUAGE plpgsql because LANGUAGE sql does not support runtime changes of search_path (schema elements are bound at inline time rather than runtime)

bugfix: schemas/vegbien.sql: functions with schema_anchors: must use plpgsql for these because the sql language does not support runtime changes of search_path (the schema elements they use are bound at inline time rather than runtime)

schemas/vegbien.sql: schema_null param: renamed to schema_anchor to clarify what this is for

fix: schemas/vegbien.sql: schema_null: clarified that this should always be left as the default value, not just usually

schemas/vegbien.sql: schema_null params: use schema_anchor instead of source for this, since it is guaranteed to exist regardless of which tables are in the VegBIEN schema

schemas/vegbien.sql: public: added schema_anchor (used with schema_null params)

schemas/util.sql: use new util.debug_print_sql() instead of `RAISE NOTICE` to improve readability of the debug output (which is used throughout the runscripts)

schemas/util.sql: added debug_print_sql()

schemas/util.sql: added raise_notice(), to allow NOTICEs to be raised in sql-language functions