openingd/json_fund_channel:

- result fundchannel command now depends on successful or failed broadcast of the funding tx
- failure returns error code FUNDING_BROADCAST_FAIL
- don't fail the channel when broadcast failed, but keep in CHANNELD_AWAITING_LOCKIN
- after fixing the initial broadcast failure, the user could manually rebroadcast the tx and
  keep the channel

openingd/opening_funder_finished:
- broadcast_tx callback function now handles both success and failure

jsonrpc: added error code FUNDING_BROADCAST_FAIL
manpage: added error code returned by fundchannel command

This makes the user more aware of broadcast failure, so it hopefully doesn't
try to broadcast new tx's that depend on its change_outputs. Some users have reported (see
issue #2171) a whole sequence of fundings failing, because each funding was using the change
output of the previous one, which would not confirm.

common/jsonrpc_errors.h

@@ -39,6 +39,7 @@
 #define FUND_MAX_EXCEEDED               300
 #define FUND_CANNOT_AFFORD              301
 #define FUND_OUTPUT_IS_DUST             302
+#define FUNDING_BROADCAST_FAIL          303
 
 /* Errors from `invoice` command */
 #define INVOICE_LABEL_ALREADY_EXISTS	900