Trigger -alertnotify if network is upgrading without you

This adds a -regetest-only undocumented (for regression testing only)
command-line option -blockversion=N to set block.nVersion.

Adds to the "has the rest of the network upgraded to a
block.nVersion we don't understand" code so it calls
-alertnotify when 51 of the last 100 blocks are up-version.
But it only alerts once, not with every subsequent new, upversion
block.

And adds a forknotify.py regression test to make sure it works.

Tested using forknotify.py:

Before adding CAlert::Notify, get:
Assertion failed: -alertnotify did not warn of up-version blocks

Before adding code to only alert once:
Assertion failed: -alertnotify excessive warning of up-version blocks

After final code in this pull:
Tests successful

1 files changed, 65 insertions, 0 deletions

diff --git a/qa/rpc-tests/forknotify.py b/qa/rpc-tests/forknotify.py
new file mode 100755
index 0000000000..a482f7cc5a
--- /dev/null
+++ b/qa/rpc-tests/forknotify.py
@@ -0,0 +1,65 @@
+#!/usr/bin/env python
+# Copyright (c) 2014 The Bitcoin Core developers
+# Distributed under the MIT/X11 software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#
+# Test -alertnotify 
+#
+
+from test_framework import BitcoinTestFramework
+from bitcoinrpc.authproxy import AuthServiceProxy, JSONRPCException
+from util import *
+import os
+import shutil
+
+class ForkNotifyTest(BitcoinTestFramework):
+
+    alert_filename = None  # Set by setup_network
+
+    def setup_network(self, test_dir):
+        nodes = []
+        self.alert_filename = os.path.join(test_dir, "alert.txt")
+        with open(self.alert_filename, 'w') as f:
+            pass  # Just open then close to create zero-length file
+        nodes.append(start_node(0, test_dir,
+                            ["-blockversion=2", "-alertnotify=echo %s >> '" + self.alert_filename + "'"]))
+        # Node1 mines block.version=211 blocks
+        nodes.append(start_node(1, test_dir,
+                                ["-blockversion=211"]))
+        connect_nodes(nodes[1], 0)
+
+        sync_blocks(nodes)
+        return nodes
+        
+
+    def run_test(self, nodes):
+        # Mine 51 up-version blocks
+        nodes[1].setgenerate(True, 51)
+        sync_blocks(nodes)
+        # -alertnotify should trigger on the 51'st,
+        # but mine and sync another to give
+        # -alertnotify time to write
+        nodes[1].setgenerate(True, 1)
+        sync_blocks(nodes)
+
+        with open(self.alert_filename, 'r') as f:
+            alert_text = f.read()
+
+        if len(alert_text) == 0:
+            raise AssertionError("-alertnotify did not warn of up-version blocks")
+
+        # Mine more up-version blocks, should not get more alerts:
+        nodes[1].setgenerate(True, 1)
+        sync_blocks(nodes)
+        nodes[1].setgenerate(True, 1)
+        sync_blocks(nodes)
+
+        with open(self.alert_filename, 'r') as f:
+            alert_text2 = f.read()
+
+        if alert_text != alert_text2:
+            raise AssertionError("-alertnotify excessive warning of up-version blocks")
+
+if __name__ == '__main__':
+    ForkNotifyTest().main()