Add a new checkpoint at block 279,000

From a cursory glance, it looks like block 279,000 meets the criteria for
a checkpoint block, and it's also what the bootstrap.dat torrent is at. This closes #3530.

src/checkpoints.cpp

@@ -1,4 +1,4 @@
-// Copyright (c) 2009-2013 The Bitcoin developers
+// Copyright (c) 2009-2014 The Bitcoin developers
 // Distributed under the MIT/X11 software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -50,11 +50,12 @@ namespace Checkpoints
         (216116, uint256("0x00000000000001b4f4b433e81ee46494af945cf96014816a4e2370f11b23df4e"))
         (225430, uint256("0x00000000000001c108384350f74090433e7fcf79a606b8e797f065b130575932"))
         (250000, uint256("0x000000000000003887df1f29024b06fc2200b55f8af8f35453d7be294df2d214"))
+        (279000, uint256("0x0000000000000001ae8c72a0b0c301f67e3afca10e819efa9041e458e9bd7e40"))
         ;
     static const CCheckpointData data = {
         &mapCheckpoints,
-        1375533383, // * UNIX timestamp of last checkpoint block
-        21491097,   // * total number of transactions between genesis and last checkpoint
+        1389047471, // * UNIX timestamp of last checkpoint block
+        30549816,   // * total number of transactions between genesis and last checkpoint
                     //   (the tx=... number in the SetBestChain debug.log lines)
         60000.0     // * estimated number of transactions per day after checkpoint
     };
@@ -111,7 +112,7 @@ namespace Checkpoints
 
         double fWorkBefore = 0.0; // Amount of work done before pindex
         double fWorkAfter = 0.0;  // Amount of work left after pindex (estimated)
-        // Work is defined as: 1.0 per transaction before the last checkoint, and
+        // Work is defined as: 1.0 per transaction before the last checkpoint, and
         // fSigcheckVerificationFactor per transaction after.
 
         const CCheckpointData &data = Checkpoints();