LastTip() and tweak deprecation heights

src/chain.h

@@ -416,6 +416,7 @@ public:
 class CChain {
 private:
     std::vector<CBlockIndex*> vChain;
+    CBlockIndex *lastTip;
 
 public:
     /** Returns the index entry for the genesis block of this chain, or NULL if none. */
@@ -427,6 +428,11 @@ public:
     CBlockIndex *Tip() const {
         return vChain.size() > 0 ? vChain[vChain.size() - 1] : NULL;
     }
+    
+    /** Returns the last tip of the chain, or NULL if none. */
+    CBlockIndex *LastTip() const {
+        return vChain.size() > 0 ? lastTip : NULL;
+    }
 
     /** Returns the index entry at a particular height in this chain, or NULL if no such height exists. */
     CBlockIndex *operator[](int nHeight) const {