I started playing with simnet and was confronted with error message:

```
[ERR] FNDG: Unable to broadcast funding tx for ChannelPoint(<point>:0):
-22: TX rejected: transaction <tx> has witness data, but segwit isn't active yet
```

I wasn't aware of the activation period so I got quite puzzled.
Google helped. But I think the message could mention likely cause.

Newly it optionally prints something like:

```
(The threshold for segwit activation is 300 blocks on simnet, current best height is 113)
```

test go 1.14
use golangci-lint

This change makes btcd's getblock command match bitcoind's. Previously
the default verbosity was 0, which caused errors when using the
rpcclient library to connect to a bitcoind node - getblock would
unmarshall incorrectly since it didn't expect a verbosity=1 result when
it did not specify verbosity.

Without this, users of this library wouldn't be able to issue GetBlock
requests to nodes which haven't updated to support the latest request
format, namely the use of a single `int` parameter to denote verbosity
instead of two `bool`s.

build: multiple cleanups

rpcclient: send legacy GetBlock request for backwards compatibility

Based on Hugo Landau's cookie auth implementation for Namecoin's ncdns.

Fixes btcsuite#1054

Remove unnecessary slice of all block indexes and
remove DB iteration over all block indexes that
used to determined the size of the slice.

…point

The current methods to add to a UtxoViewpoint don't allow for a situation where
we have only UTXO data but not a whole transaction.  This commit allows
contstruction of a UtxoEntry without requiring a full MsgTx.

AddTxOut() and AddTxOuts() both require a whole transaction, including the inputs,
which are only used in order to calculate the txid.  In some situations, such as
with use of the utreexo accumulator, we only have the utxo data but not the
transaction which created it.

For reference, utreexo's initial usage of the blockchain.NewUtxoEntry() function is at
https://github.com/mit-dci/utreexo/pull/135/files#diff-3f7b8f9991ea957f1f4ad9f5a95415f0R96

While here, also rename and generalize limitMap and apply to
other maps which need to be bounded.

The implementation has been adapted from the dcrec module in dcrd. The
bug was initially fixed in decred/dcrd@3d9cda1 while transitioning to a
constant time algorithm. A large set of test vectors were subsequently
added in decred/dcrd@8c6b52d.

The function signature has been preserved for backwards compatibility.
This means that returning whether the value has overflowed, and the
corresponding test vectors have not been backported.

This fixes btcsuite#1170 and closes a previous attempt to fix the bug in btcsuite#1178.

To run integration tests with btcd on Windows in non-interactive
environments (such as the Travis build with Windows machines), we
need to make sure we can still spawn a child process instead of only a
windows background service.

Corrections suggested by @onyb btcsuite#1608 (comment)

backport from decred/dcrd#2253

When a peer sends a notfound message, remove the hash from requested
map.  Also increase notfound ban score and return early if it
disconnects the peer.

config+service_windows: add flag to disable win service

- remove prep_release.sh and notes.sample
- update license in release.sh
- add notes for maintainers on the release process
- mention CHANGES file modifications

Also updated changes for 0.20.1, and added a small note about changes
since 0.12.0.