Block height in coinbase as a new block rule

"Version 2" blocks are blocks that have nVersion=2 and
have the block height as the first item in their coinbase.
Block-height-in-the-coinbase is strictly enforced when
version=2 blocks are a supermajority in the block chain
(750 of the last 1,000 blocks on main net, 51 of 100 for
testnet). This does not affect old clients/miners at all,
which will continue producing nVersion=1 blocks, and
which will continue to be valid.

src/main.h

@@ -820,7 +820,7 @@ class CBlock
 {
 public:
     // header
-    static const int CURRENT_VERSION=1;
+    static const int CURRENT_VERSION=2;
     int nVersion;
     uint256 hashPrevBlock;
     uint256 hashMerkleRoot;
@@ -1164,6 +1164,12 @@ public:
         return pindex->GetMedianTimePast();
     }
 
+    /**
+     * Returns true if there are nRequired or more blocks of minVersion or above
+     * in the last nToCheck blocks, starting at pstart and going backwards.
+     */
+    static bool IsSuperMajority(int minVersion, const CBlockIndex* pstart,
+                                unsigned int nRequired, unsigned int nToCheck);
 
 
     std::string ToString() const