A simple PostgreSQL URI type similar to http://pgfoundry.org/projects/uri that
allows efficient indexing and searching of URIs.  It was designed for storing
web browsing history and policies.  It breaks URI strings up into their scheme,
domain (itself broken up by dots and reversed for the sake of sorting), port,
and path.  URIs can be partial, with any part missing, and defines ordering and
containment relations, such that 'foo.com' @> 'http://www.foo.com/path'.