Revert my patch of 2009-04-04 that removed contrib/intarray's definitions of

Revert my patch of 2009-04-04 that removed contrib/intarray's definitions of
the <@ and @> operators.  These are not in fact equivalent to the built-in
anyarray operators of the same names, because they have different behavior for
empty arrays, namely they don't think empty arrays are contained in anything.
That is mathematically wrong, no doubt, but until we can persuade GIN indexes
to implement the mathematical definition we should probably not change this.
Another reason for not changing it now is that we can't yet ensure the
opclasses will be updated correctly in a dump-and-reload upgrade.  Per
recent discussions.