pgsql: Add support for user-defined I/O conversion casts.

Log Message:
-----------
Add support for user-defined I/O conversion casts.

Modified Files:
--------------
pgsql/doc/src/sgml:
catalogs.sgml (r2.179 -> r2.180)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/catalogs.sgml?r1=2.179&r2=2.180)
pgsql/doc/src/sgml/ref:
create_cast.sgml (r1.29 -> r1.30)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/create_cast.sgml?r1=1.29&r2=1.30)
pgsql/src/backend/commands:
functioncmds.c (r1.99 -> r1.100)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/functioncmds.c?r1=1.99&r2=1.100)
pgsql/src/backend/nodes:
copyfuncs.c (r1.409 -> r1.410)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/copyfuncs.c?r1=1.409&r2=1.410)
equalfuncs.c (r1.334 -> r1.335)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/equalfuncs.c?r1=1.334&r2=1.335)
pgsql/src/backend/parser:
gram.y (r2.632 -> r2.633)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y?r1=2.632&r2=2.633)
parse_coerce.c (r2.170 -> r2.171)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_coerce.c?r1=2.170&r2=2.171)
pgsql/src/bin/pg_dump:
pg_dump.c (r1.502 -> r1.503)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_dump.c?r1=1.502&r2=1.503)
pg_dump.h (r1.141 -> r1.142)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_dump.h?r1=1.141&r2=1.142)
pgsql/src/include/catalog:
catversion.h (r1.499 -> r1.500)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.499&r2=1.500)
pg_cast.h (r1.39 -> r1.40)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_cast.h?r1=1.39&r2=1.40)
pgsql/src/include/nodes:
parsenodes.h (r1.376 -> r1.377)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/parsenodes.h?r1=1.376&r2=1.377)
pgsql/src/test/regress/expected:
opr_sanity.out (r1.84 -> r1.85)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/opr_sanity.out?r1=1.84&r2=1.85)
pgsql/src/test/regress/sql:
opr_sanity.sql (r1.68 -> r1.69)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/opr_sanity.sql?r1=1.68&r2=1.69)