Merge pull request #1869 from Gustav-Simonsson/gpu_miner

all: Add GPU mining, disabled by default

core/chain_makers.go

@@ -32,7 +32,7 @@ import (
 // It returns true from Verify for any block.
 type FakePow struct{}
 
-func (f FakePow) Search(block pow.Block, stop <-chan struct{}) (uint64, []byte) {
+func (f FakePow) Search(block pow.Block, stop <-chan struct{}, index int) (uint64, []byte) {
 	return 0, nil
 }
 func (f FakePow) Verify(block pow.Block) bool { return true }