pgsql: Document that pg_dump -d/-D prevents invalid data from canceling

Log Message:
-----------
Document that pg_dump -d/-D prevents invalid data from canceling the
entire table load.

Modified Files:
--------------
pgsql/doc/src/sgml/ref:
pg_dump.sgml (r1.82 -> r1.83)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/pg_dump.sgml.diff?r1=1.82&r2=1.83)