Add :concurrently option to Database#refresh_view on PostgreSQL to support concurrent refresh of materialized views

This is supported starting in PostgreSQL 9.4.
Add :check option to Database#create_view for WITH [LOCAL] CHECK OPTION support

PostgreSQL 9.4 adds support for this SQL standard option, but
as many databases implement it, it should be a core option.
Add Postgres::ArrayOp#cardinality to the pg_array_ops extension

This is supported starting in PostgreSQL 9.4.
Allow Postgres::ArrayOp#unnest to accept arguments in the pg_array_ops extension

PostgreSQL 9.4 allows this, but only if unnest is used in the FROM
clause.
Support PostgreSQL 9.4+ jsonb type in the pg_json extension

There are not implicit casts between the json and jsonb types,
so Sequel needs to basically separate the two and use different
classes for each.  So you have to use Sequel.pg_jsonb to get
a jsonb type.

Note that this does not include support for the new jsonb
functions in pg_json_ops.  For some reason, instead of keeping
the function names the same and just varying the type, they
had duplicate functions.  Hopefully this will change before the
official release of PostgreSQL 9.4.