Make Row type comparable

This PR addresses #1957 to make ``row`` type comparable and implements the ``EQUAL`` and ``NOT_EQUAL`` operators for the ``row`` type.
You need to use elementType.hash() here, otherwise two equal rows could have different hash codes. Try it with something like:  `row<timestamp with time zone>` and test that these two are equal and have the same hash:
`timestamp '2012-10-31 08:00 UTC'`
`timestamp '2012-10-31 01:00 America/Los_Angeles'`