leveldb: use 'comma ok' on iterator.ErrorCallbackSetter type assertion (fixes #101)
leveldb: use 'comma ok' on iterator.ErrorCallbackSetter type assertion (fixes #101)

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