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/tcop/pquery.c

@@ -1186,9 +1186,10 @@ PortalRunUtility(Portal portal, Node *utilityStmt, bool isTopLevel,
 	ProcessUtility(utilityStmt,
 				   portal->sourceText,
 				   portal->portalParams,
-				   isTopLevel,
 				   dest,
-				   completionTag);
+				   completionTag,
+				   isTopLevel ?
+					PROCESS_UTILITY_TOPLEVEL : PROCESS_UTILITY_QUERY);
 
 	/* Some utility statements may change context on us */
 	MemoryContextSwitchTo(PortalGetHeapMemory(portal));