Track modified size in TxMemPoolEntry so that we can correctly compute priority.

src/core.h

@@ -284,6 +284,9 @@ public:
     // Compute priority, given priority of inputs and (optionally) tx size
     double ComputePriority(double dPriorityInputs, unsigned int nTxSize=0) const;
 
+    // Compute modified tx size for priority calculation (optionally given tx size)
+    unsigned int CalculateModifiedSize(unsigned int nTxSize=0) const;
+
     bool IsCoinBase() const
     {
         return (vin.size() == 1 && vin[0].prevout.IsNull());