Replace the 200ms polling loop with a faster and more efficient waiting
operation.
This was tried a few times before, but given up every time because
solutions use a condition variable which is not safe for use in signals
as they need to be reentrant.
On UNIX-ish OSes, use a safe way: a pipe. When shutdown is requested
write a dummy byte to the pipe. Waiting for shutdown is a matter of a
blocking read from the pipe.
On Windows, there are no signals so using a condition variable is safe.
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
