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, fixes compatibility with LibreSSL, 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
• Build against system UniValue when available
• Use system univalue by default
• LibreSSL doesn't define OPENSSL_VERSION, use LIBRESSL_VERSION_TEXT instead
• Bugfix: Only use git for build info if the repository is actually the right one
• fixes/refactoring for building against LibreSSL

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)
• Send 'mempool' P2P command at the start of each P2P session
• Restore ability to display addresses in GUI
• [Qt] support for persisted rpc console history
• add key generation type
• Add preciousblock RPC
• [Wallet] add rescanblockchain RPC command
• Qt: Add network port input box to GUI settings
• Add option to opt into full-RBF when sending funds
• Travis: Test build against system Qt4 and without libevent
• Bugfix: Correctly calculate priority when inputs are mined after dependent transactions enter the memory pool
• [Qt] add InMempool() info to transaction details
• rpc: remove cs_main lock from `createrawtransaction`
• [RPC] Add RBF opt-in possibilities to rawtx functions
• Unify product name to as few places as possible
• Make RBF policies optional
• Reduce inefficiency of GetAccountAddress()
• [RPC] Expose ancestor/descendant information over RPC
• [trivial] fixing multiple typos
• Banlist updates
• Render icons from SVG
• Workaround Travis-side CI issues
• Common argument defaults for NODE_BLOOM stuff and -wallet
• Read/write bitcoin_rw.conf for exposing shared Daemon/GUI options in the GUI
• Add change options to fundrawtransaction
• RPC: sendrawtransaction: Allow the user to ignore/override specific rejections
• rpc: Input-from-stdin mode for bitcoin-cli
• Add importmulti RPC call

Improved pattern-matching spam filter

Bitcoin Knots includes a 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.