Make new event trigger facility actually do something.

Commit 3855968f32 added syntax, pg_dump,
psql support, and documentation, but the triggers didn't actually fire.
With this commit, they now do.  This is still a pretty basic facility
overall because event triggers do not get a whole lot of information
about what the user is trying to do unless you write them in C; and
there's still no option to fire them anywhere except at the very
beginning of the execution sequence, but it's better than nothing,
and a good building block for future work.

Along the way, add a regression test for ALTER LARGE OBJECT, since
testing of event triggers reveals that we haven't got one.

Dimitri Fontaine and Robert Haas

src/backend/commands/trigger.c

@@ -1026,7 +1026,7 @@ ConvertTriggerToFK(CreateTrigStmt *stmt, Oid funcoid)
 		/* ... and execute it */
 		ProcessUtility((Node *) atstmt,
 					   "(generated ALTER TABLE ADD FOREIGN KEY command)",
-					   NULL, false, None_Receiver, NULL);
+					   NULL, None_Receiver, NULL, PROCESS_UTILITY_GENERATED);
 
 		/* Remove the matched item from the list */
 		info_list = list_delete_ptr(info_list, info);