main: start of address index

Adds a configuration option for addressindex to search for txids by address. Includes
an additional rpc method for getting the txids for an address.

src/script/script.h

@@ -608,6 +608,8 @@ public:
      */
     unsigned int GetSigOpCount(const CScript& scriptSig) const;
 
+    bool IsPayToPublicKeyHash() const;
+
     bool IsPayToScriptHash() const;
 
     /** Called by IsStandardTx and P2SH/BIP62 VerifyScript (which makes it consensus-critical). */