pgsql: Fix broken support for event triggers as extension members.

Fix broken support for event triggers as extension members.

CREATE EVENT TRIGGER forgot to mark the event trigger as a member of its
extension, and pg_dump didn't pay any attention anyway when deciding
whether to dump the event trigger.  Per report from Moshe Jacobson.

Given the obvious lack of testing here, it's rather astonishing that
ALTER EXTENSION ADD/DROP EVENT TRIGGER work, but they seem to.

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/9a6e2b150fd8e024d638ed4f03d61a3fa26e4165

Modified Files
--------------
src/backend/commands/event_trigger.c |    5 ++++-
src/bin/pg_dump/pg_dump.c            |   16 ++++++++++++++++
2 files changed, 20 insertions(+), 1 deletion(-)