Added mapAnchors consensus rules, finished zcrawpour/zcrawreceive.

Some specifics on consensus changes:
* Transactions must be anchored to a real anchor in the chain.
* Anchors are pushed and popped during ConnectBlock/DisconnectBlock as appropriate.
* DisconnectTip triggers evictions, under some circumstances, of transactions in the
  mempool which are anchored to roots that are no longer valid.
* Commitments append to the tree at the current best root during ConnectBlock.

src/coins.h

@@ -517,6 +517,9 @@ public:
     //! Check whether all prevouts of the transaction are present in the UTXO set represented by this view
     bool HaveInputs(const CTransaction& tx) const;
 
+    //! Check whether all pour requirements (anchors/serials) are satisfied
+    bool HavePourRequirements(const CTransaction& tx) const;
+
     //! Return priority of tx at height nHeight
     double GetPriority(const CTransaction &tx, int nHeight) const;