rpc: have fundchannel_start also return scriptpubkey

Easier to pass it back than dig it out of the address, since we
have it. Needed for extracting fundchannel

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 - JSON API: `listfunds` now lists a blockheight for confirmed transactions
+- JSON API: `fundchannel_start` result now includes field `scriptpubkey`
 
 - bolt11: support for parsing feature bits (field `9`).
 

doc/lightning-fundchannel_start.7

@@ -34,7 +34,7 @@ transaction before that can lead to unrecoverable loss of funds\.
 
 .SH RETURN VALUE
 
-On success, returns the \fIfunding_address\fR for the channel\.
+On success, returns the \fIfunding_address\fR and the \fIscriptpubkey\fR for the channel funding output\.
 
 
 On failure, returns an error\.

doc/lightning-fundchannel_start.7.md

@@ -32,7 +32,7 @@ transaction before that can lead to unrecoverable loss of funds.
 RETURN VALUE
 ------------
 
-On success, returns the *funding\_address* for the channel.
+On success, returns the *funding\_address* and the *scriptpubkey* for the channel funding output.
 
 On failure, returns an error.
 

lightningd/opening_control.c

@@ -343,8 +343,10 @@ static void funding_started_success(struct funding_channel *fc,
 	out = encode_scriptpubkey_to_addr(cmd,
 				          get_chainparams(cmd->ld)->bip173_name,
 					  scriptPubkey);
-	if (out)
+	if (out) {
 		json_add_string(response, "funding_address", out);
+		json_add_hex_talarr(response, "scriptpubkey", scriptPubkey);
+	}
 
 	/* Clear this so cancel doesn't think it's still in progress */
 	fc->cmd = NULL;