Add sweepaccount tool.

[jrick]

This tool creates on-chain transactions, one per used address in a
source account, to sweep all output value to new addresses in a
different destination account.

This is a cherry-pick of the btcwallet commit 4ee9ce5.

[cjepson]

One improvement would be to use a readme.go to explain the utility.

[jcvernaleo]

I've used it with btcwallet so I'm definitely in favor of the tool.
I agree with @cjepson that a readme (or mention in the docs somewhere) would be helpful.
Also, is there a reason that this lacks -P, --password= or rpcpassword like all the other tools?
Other than those two things it looks good to me.

[jrick]

The tool can only be used interactively on the command line so I think it's fine to require typing in the rpc password in a prompt that doesn't echo.

[jrick]

Regarding docs, this tool is really only useful with the current account setup where the imported account can not create change addresses. This allows moving those funds from the imported account to another account (and this is why it defaults the source account to the imported account).

Since imported funds can now be spent (change addresses are derived for account 0) and the imported account is planned to be removed (where every account can have imported keys) there is less need for this tool and I would be wary about encouraging its long term use.

I can add doco later, but it should cover these details and we may even decide to remove the tool later once the accounts situation has been fixed.

[jcvernaleo]

I can live with that then.
OK

[JFixby]

Is there a documentation on how to use it?

dcrctl --wallet sweepaccount default Da1b2c3d4e5f6g7h produces some json. Not sure what to do with it.

[chappjc]

@JFixby it gives an unsigned transaction: "unsignedtransaction": "value", (string) The hex encoded string of the unsigned transaction.
You then can decode it to inspect it, and sign and send it. See either signrawtransaction plus sendrawtransaction, or signrawtransactions .