Packaging cleanups ("syslibs")

Adds options to build using system LevelDB, libsecp256k1, and UniValue libraries, and/or without the libevent library (see ./configure --help for usage).

Please note this may be dangerous and make theft from you possible if used with versions of the LevelDB or libsecp256k1 libraries which have not been audited to meet the bug-for-bug compatibility required by Bitcoin's consensus protocol. These options are disabled by default for this reason.

It also adds options to disable building bitcoin-cli or bitcoin-tx individually, and avoids involving foreign git trees in the build.

See also:

• configure: BITCOIN_SUBDIR_TO_INCLUDE: Improve compatibility with paths including space and multiline cpp output
• Support for building against system LevelDB
• configure: Add unsupported --with-system-libsecp256k1 configure flag
• configure: Make it possible to build only one of bitcoin-cli or bitcoin-tx
• Support building without libevent
• Use system univalue by default
• Bugfix: Only use git for build info if the repository is actually the right one

Functional and policy enhancements

This is a collection of fixes, and various other improvements:

• Parse URIs with non-BTC amounts
• -acceptnonstdtxn option to skip "non-standard transaction" checks
• Support for Tonal Bitcoin units (ᵇTBC, ˢTBC, and TBC)
• Restore ability to display addresses in GUI
• [Qt] support for persisted rpc console history
• add key generation type
• [Wallet] add rescanblockchain RPC command
• Qt: Add network port input box to GUI settings
• Travis: Test build against system Qt4 and without libevent
• Bugfix: Correctly calculate priority when inputs are mined after dependent transactions enter the memory pool
• Make RBF policies optional
• Render icons from SVG
• Read/write bitcoin_rw.conf for exposing shared Daemon/GUI options in the GUI
• RPC: sendrawtransaction: Allow the user to ignore/override specific rejections
• Add witness data output to TxInError messages
• Add mempool statistics collector
• [Qt] Add interactive mempool graph
• Basic multiwallet support
• [RPC] Transaction details in getblock
• RPC: Add parameter to addmultisigaddress / createmultisig to sort public keys
• RPC refactoring: Never access wallet directly, only via new CRPCRequestInfo
• Add query options to listunspent RPC call
• Enable various p2sh-p2wpkh functionality
• Wallet/RPC: sweepprivkeys method to scan UTXO set and send to local wallet
• Drop IO priority to idle while reading blocks for getblock requests
• Add test for CWalletTx::GetImmatureCredit() returning stale values.
• Refactor mempool.dat to be extensible, and store missing info
• [Qt] Show more significant warning if we fall back to the default fee
• Fix CCheckQueue IsIdle (potential) race condition
• CCheckQueue Unit Tests
• [Qt][RPC] Autocomplete commands for 'help' command in debug console
• listreceivedbyaddress Filter Address
• [RPC] dumpmasterprivkey command
• rpc: Don't FlushStateToDisk when pruneblockchain(0)
• [net] Avoid possibility of NULL pointer dereference in MarkBlockAsInFlight(...)
• RPC: getblockchaininfo returns BIP signaling statistics
• [Qt] Add checkbox in the GUI to opt-in to RBF when creating a transaction
• [rpc] listsinceblock should include lost transactions when parameter is a reorg'd block
• Opt-into-RBF for RPC & bitcoin-tx
• Qt/Intro: Add explanation of IBD process
• Add friendly output to dumpwallet
• If -spkreuse=0, ensure transactions in mempool always have unique scriptPubKeys
• Qt: Network Watch tool
• tests: Fix dangling pwalletMain pointer in wallet tests
• Make most policy options configurable in GUI Options, and add "corepolicy" option to use Bitcoin Core defaults
• Trivially map blockmaxsize to blockmaxweight while segwit is unactivated
• Restore original bytespersigop as bytespersigopstrict
• Multiwallet RPC support
• Multiwallet GUI support

Improved pattern-matching spam filter

Bitcoin Knots includes an optional policy change that improves the spam filtering capabilities using matching of patterns identified in spam.

Specifically, spam created by the following are identified and ignored:

• BetCoin Dice
• Correct Horse Battery Staple
• Old spammy Counterparty encoding (NOT current versions of Counterparty)
• Lucky Bit
• Mastercoin
• SatoshiBones
• SatoshiDICE

Note that the organizations and people responsible for the spam are not filtered, only the spam itself. This feature can be disabled using the -spamfilter=0 command-line option, or in the GUI Options dialog.