bitcoin: add weight calculation helpers.

These are pulled from wallet/wallet.c, with the fix now that we grind sigs.

This reduces the fees we pay slightly, as you can see in the coinmoves changes.

I now print out all the coin moves in suitable format before we match:
you only see this if the test fails, but it's really helpful.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/utxo.c

@@ -113,3 +113,8 @@ struct bitcoin_tx *tx_spending_utxos(const tal_t *ctx,
 
 	return tx;
 }
+
+size_t utxo_spend_weight(const struct utxo *utxo)
+{
+	return bitcoin_tx_simple_input_weight(utxo->is_p2sh);
+}

common/utxo.h

@@ -59,4 +59,6 @@ struct bitcoin_tx *tx_spending_utxos(const tal_t *ctx,
 				     u32 nlocktime,
 				     u32 nsequence);
 
+/* Estimate of (signed) UTXO weight in transaction */
+size_t utxo_spend_weight(const struct utxo *utxo);
 #endif /* LIGHTNING_COMMON_UTXO_H */