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/extension.c

@@ -749,9 +749,9 @@ execute_sql_string(const char *sql, const char *filename)
 				ProcessUtility(stmt,
 							   sql,
 							   NULL,
-							   false,	/* not top level */
 							   dest,
-							   NULL);
+							   NULL,
+							   PROCESS_UTILITY_QUERY);
 			}
 
 			PopActiveSnapshot();