Accounts integration

Conflicts:
	cmd/blocktest/main.go
	cmd/mist/debugger.go
	cmd/utils/cmd.go

Help for a specific command now shows available subcommands.

Add empty total difficulty to test blocks and clean up stopping the node

Poc9/cli (exportchain)

[WIP] Poc9/natspec

Merge branch 'accounts-integration' of https://github.com/fjl/go-ethereum into fjl-accounts-integration

The interface has moved to package xeth because that's where it is
actually used.

Conflicts:
	cmd/utils/cmd.go
	cmd/utils/flags.go
	core/manager.go
	eth/backend.go
	rpc/http/server.go
	xeth/xeth.go