pg_dump fails on domain constraint comments

Hello Alvaro,

It looks like pg_dump emits incorrect text for domain constraint comments:

Assuming the following structure,

CREATE DOMAIN "dom" AS integer
        CONSTRAINT "dom_constraint" CHECK ((VALUE > 10));

COMMENT ON CONSTRAINT "dom_constraint" ON DOMAIN "dom" IS 'domain constraint comment'

pg_dump will dump the COMMENT as follow:

COMMENT ON CONSTRAINT "dom_constraint" ON DOMAIN """dom""" IS 'domain constraint comment'

Note the double-quoting issue of the domain name.

Attached patch fixes that.

                                    Elvis