Merge pull request #1428 from obscuren/coinbase-fixes

cmd/geth/main.go

cmd/utils/flags.go

eth/backend.go

miner/miner.go

miner/worker.go

rpc/api/miner.go

rpc/api/miner_args.go

rpc/api/miner_js.go

tests/block_test_util.go

tests/state_test_util.go

xeth/types.go

xeth/xeth.go