pgsql: Fix pg_dump to dump shell types.

Fix pg_dump to dump shell types.

Per discussion, it really ought to do this. The original choice to
exclude shell types was probably made in the dark ages before we made
it harder to accidentally create shell types; but that was in 7.3.

Also, cause the standard regression tests to leave a shell type behind,
for convenience in testing the case in pg_dump and pg_upgrade.

Back-patch to all supported branches.

Branch
------
REL9_5_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/1f507c7e9dc5b2e8373018fea2f002531c9c1d3a

Modified Files
--------------
src/bin/pg_dump/pg_dump.c | 77 ++++++++++++++++++++++++++---
src/bin/pg_dump/pg_dump.h | 2 +-
src/test/regress/expected/create_type.out | 2 +
src/test/regress/sql/create_type.sql | 3 ++
4 files changed, 77 insertions(+), 7 deletions(-)