reenable known-case after return optimization for Grin.
reenable known-case after return optimization for Grin.

darcs-hash:20070606123308-1a7c6-2a1bd6684465a9954d69223344496800608b6993

kirbyfan64/jhc,kirbyfan64/jhc,kirbyfan64/jhc,kirbyfan64/jhc