Low-level RPC changes

- Error codes have been updated to be more accurate for the following error cases:

- `getblock` now returns RPC_MISC_ERROR if the block can't be found on disk (for

example if the block has been pruned). Previously returned RPC_INTERNAL_ERROR.

- `pruneblockchain` now returns RPC_MISC_ERROR if the blocks cannot be pruned

because the node is not in pruned mode. Previously returned RPC_METHOD_NOT_FOUND.

- `pruneblockchain` now returns RPC_INVALID_PARAMETER if the blocks cannot be pruned

because the supplied timestamp is too late. Previously returned RPC_INTERNAL_ERROR.

- `pruneblockchain` now returns RPC_MISC_ERROR if the blocks cannot be pruned

because the blockchain is too short. Previously returned RPC_INTERNAL_ERROR.

- `setban` now returns RPC_CLIENT_INVALID_IP_OR_SUBNET if the supplied IP address

or subnet is invalid. Previously returned RPC_CLIENT_NODE_ALREADY_ADDED.

- `setban` now returns RPC_CLIENT_INVALID_IP_OR_SUBNET if the user tries to unban

a node that has not previously been banned. Previously returned RPC_MISC_ERROR.

- `removeprunedfunds` now returns RPC_WALLET_ERROR if bitcoind is unable to remove

the transaction. Previously returned RPC_INTERNAL_ERROR.

- `removeprunedfunds` now returns RPC_INVALID_PARAMETER if the transaction does not

exist in the wallet. Previously returned RPC_INTERNAL_ERROR.

- `fundrawtransaction` now returns RPC_INVALID_ADDRESS_OR_KEY if an invalid change

address is provided. Previously returned RPC_INVALID_PARAMETER.

- `fundrawtransaction` now returns RPC_WALLET_ERROR if bitcoind is unable to create

the transaction. The error message provides further details. Previously returned

RPC_INTERNAL_ERROR.

- `bumpfee` now returns RPC_INVALID_PARAMETER if the provided transaction has

descendants in the wallet. Previously returned RPC_MISC_ERROR.

- `bumpfee` now returns RPC_INVALID_PARAMETER if the provided transaction has

descendants in the mempool. Previously returned RPC_MISC_ERROR.

- `bumpfee` now returns RPC_WALLET_ERROR if the provided transaction has

has been mined or conflicts with a mined transaction. Previously returned

RPC_INVALID_ADDRESS_OR_KEY.

- `bumpfee` now returns RPC_WALLET_ERROR if the provided transaction is not

BIP 125 replaceable. Previously returned RPC_INVALID_ADDRESS_OR_KEY.

- `bumpfee` now returns RPC_WALLET_ERROR if the provided transaction has already

been bumped by a different transaction. Previously returned RPC_INVALID_REQUEST.

- `bumpfee` now returns RPC_WALLET_ERROR if the provided transaction contains

inputs which don't belong to this wallet. Previously returned RPC_INVALID_ADDRESS_OR_KEY.

- `bumpfee` now returns RPC_WALLET_ERROR if the provided transaction has multiple change

outputs. Previously returned RPC_MISC_ERROR.

- `bumpfee` now returns RPC_WALLET_ERROR if the provided transaction has no change

output. Previously returned RPC_MISC_ERROR.

- `bumpfee` now returns RPC_WALLET_ERROR if the fee is too high. Previously returned

RPC_MISC_ERROR.

- `bumpfee` now returns RPC_WALLET_ERROR if the fee is too low. Previously returned

RPC_MISC_ERROR.

- `bumpfee` now returns RPC_WALLET_ERROR if the change output is too small to bump the

fee. Previously returned RPC_MISC_ERROR.