accounts, eth, clique, signer: support for external signer API (#18079)

* accounts, eth, clique: implement external backend + move sighash calc to backend

* signer: implement account_Version on external API

* accounts/external: enable ipc, add copyright

* accounts, internal, signer: formatting

* node: go fmt

* flags: disallow --dev in combo with --externalsigner

* accounts: remove clique-specific signing method, replace with more generic

* accounts, consensus: formatting + fix error in tests

* signer/core: remove (test-) import cycle

* clique: remove unused import

* accounts: remove CliqueHash and avoid dependency on package crypto

* consensus/clique: unduplicate header encoding

accounts/accounts_test.go

@@ -0,0 +1,32 @@
+// Copyright 2019 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package accounts
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common/hexutil"
+)
+
+func TestTextHash(t *testing.T) {
+	hash := TextHash([]byte("Hello Joe"))
+	want := hexutil.MustDecode("0xa080337ae51c4e064c189e113edd0ba391df9206e2f49db658bb32cf2911730b")
+	if !bytes.Equal(hash, want) {
+		t.Fatalf("wrong hash: %x", hash)
+	}
+}