Allow GRANT TRIGGER privilege to DROP TRIGGER (Re: Bug ##7716)

I'd reported a few years ago what seemed an inconsistency with the TRIGGER
permission on tables where it allows a role to create a trigger but not to
drop it. I don't have the original email to reply directly to the thread
anymore, but I've moved on to actually trying to fix it myself, hence
sending to this list instead.

Original thread -
http://www.postgresql.org/message-id/E1TeaD4-0004le-Vd@wrigleys.postgresql.org

I found RemoveTriggerById() in backend/commands/trigger.c which seems to
be the code that actually drops the trigger. And I see in CreateTrigger()
above it how to use pg_class_aclcheck() to check for valid permissions, so
I was going to see about adding that code to the Remove section. However, I
see no code in Remove for checking for object ownership, so I'm not sure
how that is being enforced currently which would also have to be adjusted.
I see down in RangeVarCallbackForRenameTrigger() that it uses
pg_class_ownercheck() to do so, but can't find where that is being done for
dropping a trigger.

I've tried tracing the function calls in RemoveTriggerById() to see if one
of them is doing the owner check, but I haven't been able to see it. The
only other reference to RemoveTriggerById() I can find is in
backend/catalog/dependency.c and I don't see the check there either.

This is my first time really digging into the postgres core code to try and
adjust something myself. Even if there's no interest in accepting a patch
for this, I would appreciate some guidance on how to go about it.

Thanks!

--
Keith Fiske
Database Administrator
OmniTI Computer Consulting, Inc.
http://www.keithf4.com