Make CBlockIndex* returned by GetDepthInMainChain const.

Make the CBlockIndex* (optionally) returned by GetDepthInMainChain
const.  This prevents accidental modification.  The result is for
reading its properties rather than modifying it.

src/wallet.cpp

@@ -2298,7 +2298,7 @@ int CMerkleTx::SetMerkleBranch(const CBlock& block)
     return chainActive.Height() - pindex->nHeight + 1;
 }
 
-int CMerkleTx::GetDepthInMainChainINTERNAL(CBlockIndex* &pindexRet) const
+int CMerkleTx::GetDepthInMainChainINTERNAL(const CBlockIndex* &pindexRet) const
 {
     if (hashBlock == 0 || nIndex == -1)
         return 0;
@@ -2324,7 +2324,7 @@ int CMerkleTx::GetDepthInMainChainINTERNAL(CBlockIndex* &pindexRet) const
     return chainActive.Height() - pindex->nHeight + 1;
 }
 
-int CMerkleTx::GetDepthInMainChain(CBlockIndex* &pindexRet) const
+int CMerkleTx::GetDepthInMainChain(const CBlockIndex* &pindexRet) const
 {
     AssertLockHeld(cs_main);
     int nResult = GetDepthInMainChainINTERNAL(pindexRet);

src/wallet.h

@@ -474,7 +474,7 @@ struct COutputEntry
 class CMerkleTx : public CTransaction
 {
 private:
-    int GetDepthInMainChainINTERNAL(CBlockIndex* &pindexRet) const;
+    int GetDepthInMainChainINTERNAL(const CBlockIndex* &pindexRet) const;
 
 public:
     uint256 hashBlock;
@@ -519,9 +519,9 @@ public:
     // -1  : not in blockchain, and not in memory pool (conflicted transaction)
     //  0  : in memory pool, waiting to be included in a block
     // >=1 : this many blocks deep in the main chain
-    int GetDepthInMainChain(CBlockIndex* &pindexRet) const;
-    int GetDepthInMainChain() const { CBlockIndex *pindexRet; return GetDepthInMainChain(pindexRet); }
-    bool IsInMainChain() const { CBlockIndex *pindexRet; return GetDepthInMainChainINTERNAL(pindexRet) > 0; }
+    int GetDepthInMainChain(const CBlockIndex* &pindexRet) const;
+    int GetDepthInMainChain() const { const CBlockIndex *pindexRet; return GetDepthInMainChain(pindexRet); }
+    bool IsInMainChain() const { const CBlockIndex *pindexRet; return GetDepthInMainChainINTERNAL(pindexRet) > 0; }
     int GetBlocksToMaturity() const;
     bool AcceptToMemoryPool(bool fLimitFree=true, bool fRejectInsaneFee=true);
 };