storage: add Stat and error checks in rename for plan 9
storage: add Stat and error checks in rename for plan 9

syndtr/goleveldb,btcsuite/goleveldb,hustbill/goleveldb,rentongzhang/goleveldb,chai2010/goleveldb,ngaut/goleveldb,conseweb/goleveldb,trigrass2/goleveldb,no2key/goleveldb,zzl0/goleveldb,FactomProject/goleveldb