Break circular dependency: init -> * -> init by extracting shutdown.h

Most includers just wanted to react to pending shutdown.

This isolates access to `fRequestShutdown` and limits access to the shutdown
api functions, including the new `AbortShutdown` for setting it to `false`.

Note I originally called `AbortShutdown` `CancelShutdown` but that name was
already taken by winuser.h
https://travis-ci.org/bitcoin/bitcoin/jobs/386913329

This change also triggered a build error in bench. Fixing it required moving LIBBITCOIN_SERVER after LIBBITCOIN_WALLET in bench_bench_bitcoin_LDADD To make
server definitions in src/net.cpp available to wallet methods in
src/wallet/wallet.cpp. Specifically, solving:

  libbitcoin_wallet.a(libbitcoin_wallet_a-wallet.o): In function `CWalletTx::RelayWalletTransaction(CConnman*)':
  wallet.cpp:(.text+0x3f0e): undefined reference to `CConnman::NodeFullyConnected(CNode const*)'
  collect2: error: ld returned 1 exit status

https://travis-ci.org/bitcoin/bitcoin/jobs/392133581

Need for remaining init.h includes confirmed via a thorough search with a more
specific regex:
  \bInterrupt\(\)|\bShutdown\(\)|\bInitLogging\(\)|\bInitParameterInteraction\(\)|\bAppInitBasicSetup\(\)|\bAppInitParameterInteraction\(\)|\bAppInitSanityChecks\(\)|\bAppInitLockDataDirectory\(\)|\bAppInitMain\(\)|\bSetupServerArgs\(\)|\bLicenseInfo\(\)|g_wallet_init_interface|init.h

1 files changed, 23 insertions, 0 deletions

diff --git a/src/shutdown.cpp b/src/shutdown.cpp
new file mode 100644
index 0000000000..dec497d8ec
--- /dev/null
+++ b/src/shutdown.cpp
@@ -0,0 +1,23 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <shutdown.h>
+
+#include <atomic>
+
+static std::atomic<bool> fRequestShutdown(false);
+
+void StartShutdown()
+{
+    fRequestShutdown = true;
+}
+void AbortShutdown()
+{
+    fRequestShutdown = false;
+}
+bool ShutdownRequested()
+{
+    return fRequestShutdown;
+}