Merge pull request #1869 from Gustav-Simonsson/gpu_miner

all: Add GPU mining, disabled by default

xeth/xeth.go

@@ -474,7 +474,7 @@ func (self *XEth) ClientVersion() string {
 func (self *XEth) SetMining(shouldmine bool, threads int) bool {
 	ismining := self.backend.IsMining()
 	if shouldmine && !ismining {
-		err := self.backend.StartMining(threads)
+		err := self.backend.StartMining(threads, "")
 		return err == nil
 	}
 	if ismining && !shouldmine {