Adjust more backend functions to return OID rather than void.

This is again intended to support extensions to the event trigger
functionality.  This may go a bit further than we need for that
purpose, but there's some value in being consistent, and the OID
may be useful for other purposes also.

Dimitri Fontaine

src/include/commands/seclabel.h

@@ -24,7 +24,7 @@ extern void DeleteSharedSecurityLabel(Oid objectId, Oid classId);
 /*
  * Statement and ESP hook support
  */
-extern void ExecSecLabelStmt(SecLabelStmt *stmt);
+extern Oid ExecSecLabelStmt(SecLabelStmt *stmt);
 
 typedef void (*check_object_relabel_type) (const ObjectAddress *object,
 													   const char *seclabel);