Allow pg_upgrade to upgrade clusters that use exclusion contraints by

fixing pg_dump to properly preserve such indexes.

Backpatch to 9.1 and 9.0 (where the bug was introduced).

src/bin/pg_dump/pg_dump.c

@@ -12948,7 +12948,7 @@ dumpConstraint(Archive *fout, ConstraintInfo *coninfo)
 			exit_nicely();
 		}
 
-		if (binary_upgrade && !coninfo->condef)
+		if (binary_upgrade)
 			binary_upgrade_set_pg_class_oids(q, indxinfo->dobj.catId.oid, true);
 
 		appendPQExpBuffer(q, "ALTER TABLE ONLY %s\n",