Auto merge of #3520 - Eirik0:3327-sign-offline, r=bitcartel

Fix signing raw transactions with unsynced offline nodes

This PR address the issue in two different ways:

- In `signrawtransaction` we determine the consensus branch ID (which we then later use to construct the transaction) using the chain height. We now also consider the `APPROX_RELEASE_HEIGHT` as this is a better estimation than 0 for the height of the chain if we are unsynced. (This in and of itself solves the Overwinter signing issue).
- We have added an additional parameter to `signrawtransaction` to allow manually overriding the consensus branch ID that zcashd determines we are on. This allows users to work around corner cases where the first strategy is still insufficient.

Closes #3327.

qa/pull-tester/rpc-tests.sh

@@ -44,6 +44,7 @@ testScripts=(
     'merkle_blocks.py'
 #    'fundrawtransaction.py'
     'signrawtransactions.py'
+    'signrawtransaction_offline.py'
     'walletbackup.py'
     'key_import_export.py'
     'nodehandling.py'

qa/rpc-tests/signrawtransaction_offline.py

@@ -0,0 +1,46 @@
+#!/usr/bin/env python2
+
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import assert_equal, assert_true, initialize_chain_clean, start_node
+
+class SignOfflineTest (BitcoinTestFramework):
+    # Setup Methods
+    def setup_chain(self):
+        print "Initializing test directory " + self.options.tmpdir
+        initialize_chain_clean(self.options.tmpdir, 2)
+
+    def setup_network(self):
+        self.nodes = [ start_node(0, self.options.tmpdir, ["-nuparams=5ba81b19:10"]) ]
+        self.is_network_split = False
+        self.sync_all()
+
+    # Tests
+    def run_test(self):
+        print "Mining blocks..."
+        self.nodes[0].generate(101)
+
+        offline_node = start_node(1, self.options.tmpdir, ["-maxconnections=0", "-nuparams=5ba81b19:10"])
+        self.nodes.append(offline_node)
+
+        assert_equal(0, len(offline_node.getpeerinfo())) # make sure node 1 has no peers
+
+        privkeys = [self.nodes[0].dumpprivkey(self.nodes[0].getnewaddress())]
+        taddr = self.nodes[0].getnewaddress()
+
+        tx = self.nodes[0].listunspent()[0]
+        txid = tx['txid']
+        scriptpubkey = tx['scriptPubKey']
+
+        create_inputs = [{'txid': txid, 'vout': 0}]
+        sign_inputs = [{'txid': txid, 'vout': 0, 'scriptPubKey': scriptpubkey, 'amount': 10}]
+
+        create_hex = self.nodes[0].createrawtransaction(create_inputs, {taddr: 9.9999})
+
+        signed_tx = offline_node.signrawtransaction(create_hex, sign_inputs, privkeys)
+
+        # If we return the transaction hash, then we have have not thrown an error (success)
+        online_tx_hash = self.nodes[0].sendrawtransaction(signed_tx['hex'])
+        assert_true(len(online_tx_hash) > 0)
+
+if __name__ == '__main__':
+    SignOfflineTest().main()