-json writes the schema as JSON (docs/adbschema_json.txt). Added SERIAL8, LVARCHAR(n),
BOOLEAN, BIGSERIAL and nested SET/MULTISET/LIST/ROW (read from sysattrtypes). An unknown
type is written as UNKNOWN_TYPE_<n> and the dump continues, where it used to exit.
tools/adbschema/test-types.sh checks the types against a live database.
