Add tests for uncle timestamps and refactor timestamp type

cmd/evm/main.go

core/block_processor.go

core/block_processor_test.go

core/chain_makers.go

core/chain_manager.go

core/error.go

core/genesis.go

core/types/block.go

core/types/block_test.go

core/vm/environment.go

core/vm/instructions.go

core/vm/jit_test.go

core/vm/vm.go

core/vm_env.go

eth/handler.go

miner/worker.go

tests/block_test.go

tests/block_test_util.go

tests/files/BlockchainTests/bcUncleTest.json

tests/util.go