Add support for privileges on types

This adds support for the more or less SQL-conforming USAGE privilege
on types and domains.  The intent is to be able restrict which users
can create dependencies on types, which restricts the way in which
owners can alter types.

reviewed by Yeb Havinga

src/include/nodes/parsenodes.h

@@ -1282,13 +1282,15 @@ typedef enum GrantObjectType
 	ACL_OBJECT_RELATION,		/* table, view */
 	ACL_OBJECT_SEQUENCE,		/* sequence */
 	ACL_OBJECT_DATABASE,		/* database */
+	ACL_OBJECT_DOMAIN,			/* domain */
 	ACL_OBJECT_FDW,				/* foreign-data wrapper */
 	ACL_OBJECT_FOREIGN_SERVER,	/* foreign server */
 	ACL_OBJECT_FUNCTION,		/* function */
 	ACL_OBJECT_LANGUAGE,		/* procedural language */
 	ACL_OBJECT_LARGEOBJECT,		/* largeobject */
 	ACL_OBJECT_NAMESPACE,		/* namespace */
-	ACL_OBJECT_TABLESPACE		/* tablespace */
+	ACL_OBJECT_TABLESPACE,		/* tablespace */
+	ACL_OBJECT_TYPE				/* type */
 } GrantObjectType;
 
 typedef struct GrantStmt