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/test/regress/input/largeobject.source

@@ -12,6 +12,21 @@ CREATE TABLE lotest_stash_values (loid oid, fd integer);
 -- returns the large object id
 INSERT INTO lotest_stash_values (loid) SELECT lo_creat(42);
 
+-- Test ALTER LARGE OBJECT
+CREATE ROLE regresslo;
+DO $$
+  BEGIN
+    EXECUTE 'ALTER LARGE OBJECT ' || (select loid from lotest_stash_values)
+		|| ' OWNER TO regresslo';
+  END
+$$;
+SELECT
+	rol.rolname
+FROM
+	lotest_stash_values s
+	JOIN pg_largeobject_metadata lo ON s.loid = lo.oid
+	JOIN pg_authid rol ON lo.lomowner = rol.oid;
+
 -- NOTE: large objects require transactions
 BEGIN;
 
@@ -163,3 +178,4 @@ SELECT lo_unlink(loid) FROM lotest_stash_values;
 \lo_unlink :newloid
 
 TRUNCATE lotest_stash_values;
+DROP ROLE regresslo;