must have been a local problem. I was able to just build with with_pgcluster=yes under rm0/rm2/rm9.openpkg.net without problems (the patch 1.7.0rc5.1297 also applied fully clean)

postgresql/postgresql.spec

@@ -31,8 +31,8 @@
 %define       V_psqlodbc        08.02.0200
 %define       V_slony1          1.2.6
 %define       V_slony1_dir      1215
-%define       V_pgcluster       1.7.0rc4
-%define       V_pgcluster_dir   1285
+%define       V_pgcluster       1.7.0rc5
+%define       V_pgcluster_dir   1297
 %define       V_mysqlcompat     1.0b3
 %define       V_mysqlcompat_dir 548
 
@@ -156,7 +156,6 @@ AutoReqProv:  no
         transform = "s/^(\\d+)\/slony1-(\d+\.\d+\.\d+)$/$2.$1/; $_"
     }
     prog postgresql:pgcluster = {
-        comment   = "cs: 1.7.0rc5.1297 does not cleanly apply on 8.2.3"
         version   = %{V_pgcluster}.%{V_pgcluster_dir}
         url       = http://pgfoundry.org/frs/?group_id=1000072
         regex     = /(\d+/pgcluster-__VER__)-patch\.tar\.gz