Use uint64 for block header timestamp

cmd/evm/main.go

core/block_processor.go

core/chain_makers.go

core/chain_manager.go

core/types/block.go

core/types/block_test.go

core/vm/environment.go

core/vm/vm.go

core/vm_env.go

miner/worker.go

tests/util.go

xeth/types.go