Tighten integrity checks on ALTER TABLE ... ALTER COLUMN ... RENAME.

When a column is renamed, we recursively rename the same column in
all descendent tables.  But if one of those tables also inherits that
column from a table outside the inheritance hierarchy rooted at the
named table, we must throw an error.  The previous coding correctly
prohibited the rename when the parent had inherited the column from
elsewhere, but overlooked the case where the parent was OK but a child
table also inherited the same column from a second, unrelated parent.

For now, not backpatched due to lack of complaints from the field.

KaiGai Kohei, with further changes by me.
Reviewed by Bernd Helme and Tom Lane.

src/include/commands/tablecmds.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/commands/tablecmds.h,v 1.45 2010/01/02 16:58:03 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/commands/tablecmds.h,v 1.46 2010/02/01 19:28:56 rhaas Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -43,7 +43,7 @@ extern void renameatt(Oid myrelid,
 		  const char *oldattname,
 		  const char *newattname,
 		  bool recurse,
-		  bool recursing);
+		  int expected_parents);
 
 extern void RenameRelation(Oid myrelid,
 			   const char *newrelname,