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/executor/functions.c

@@ -783,9 +783,9 @@ postquel_getnext(execution_state *es, SQLFunctionCachePtr fcache)
 						es->qd->utilitystmt),
 					   fcache->src,
 					   es->qd->params,
-					   false,	/* not top level */
 					   es->qd->dest,
-					   NULL);
+					   NULL,
+					   PROCESS_UTILITY_QUERY);
 		result = true;			/* never stops early */
 	}
 	else