Add wallet method for finding spendable notes in a CTransaction

src/zcash/NoteEncryption.hpp

@@ -61,6 +61,8 @@ public:
     typedef boost::array<unsigned char, CLEN> Ciphertext;
     typedef boost::array<unsigned char, MLEN> Plaintext;
 
+    // Unused default constructor to make allocators happy
+    NoteDecryption() { }
     NoteDecryption(uint256 sk_enc);
 
     Plaintext decrypt(const Ciphertext &ciphertext,
@@ -68,6 +70,8 @@ public:
                       const uint256 &hSig,
                       unsigned char nonce
                      ) const;
+
+    friend inline bool operator<(const NoteDecryption& a, const NoteDecryption& b) { return a.pk_enc < b.pk_enc; }
 };
 
 uint256 random_uint256();