script: break out redeemscript->scriptsig function

We're going to finalze some redeemscripts here shortly, so break out the
ability to render an arbitrary redeemscript -> scriptsig

bitcoin/script.c

@@ -261,18 +261,30 @@ u8 *bitcoin_redeem_p2sh_p2wpkh(const tal_t *ctx, const struct pubkey *key)
 	return script;
 }
 
-u8 *bitcoin_scriptsig_p2sh_p2wpkh(const tal_t *ctx, const struct pubkey *key)
+u8 *bitcoin_scriptsig_redeem(const tal_t *ctx,
+			     const u8 *redeemscript TAKES)
 {
-	u8 *redeemscript = bitcoin_redeem_p2sh_p2wpkh(ctx, key), *script;
+	u8 *script;
 
 	/* BIP141: The scriptSig must be exactly a push of the BIP16
 	 * redeemScript or validation fails. */
 	script = tal_arr(ctx, u8, 0);
-	script_push_bytes(&script, redeemscript, tal_count(redeemscript));
+	script_push_bytes(&script, redeemscript,
+			  tal_count(redeemscript));
+
+	if (taken(redeemscript))
 		tal_free(redeemscript);
+
 	return script;
 }
 
+u8 *bitcoin_scriptsig_p2sh_p2wpkh(const tal_t *ctx, const struct pubkey *key)
+{
+	u8 *redeemscript =
+		bitcoin_redeem_p2sh_p2wpkh(NULL, key);
+	return bitcoin_scriptsig_redeem(ctx, take(redeemscript));
+}
+
 u8 **bitcoin_witness_p2wpkh(const tal_t *ctx,
 			    const struct bitcoin_signature *sig,
 			    const struct pubkey *key)

bitcoin/script.h

@@ -43,6 +43,10 @@ u8 *bitcoin_redeem_p2pkh(const tal_t *ctx, const struct pubkey *pubkey,
 /* Create the redeemscript for a P2SH + P2WPKH. */
 u8 *bitcoin_redeem_p2sh_p2wpkh(const tal_t *ctx, const struct pubkey *key);
 
+/* Create the scriptsig for a redeemscript */
+u8 *bitcoin_scriptsig_redeem(const tal_t *ctx,
+			     const u8 *redeemscript TAKES);
+
 /* Create scriptsig for p2sh-p2wpkh */
 u8 *bitcoin_scriptsig_p2sh_p2wpkh(const tal_t *ctx, const struct pubkey *key);