Add simple testcases for signing with rfc6979 extra entropy.
Add simple testcases for signing with rfc6979 extra entropy.

chfast/secp256k1,kleetus/secp256k1,instagibbs/secp256k1,libmetrocoin/secp256k1,libbitcoin/secp256k1,ChrisXin/secp256k1,rustyrussell/secp256k1,apoelstra/secp256k1,digitalbitbox/secp256k1,BTCfork/hardfork_prototype_1_mvf-bu,krzysztofwos/BitcoinUnlimited,pmienk/secp256k1,apoelstra/secp256k1,Gustav-Simonsson/secp256k1,instagibbs/secp256k1,apoelstra/secp256k1,bitcoin-core/secp256k1,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,afk11/secp256k1,marcusdiaz/BitcoinUnlimited,rustyrussell/secp256k1,shea256/secp256k1-zkp,BTCfork/hardfork_prototype_1_mvf-bu,sipa/secp256k1,cddjr/BitcoinUnlimited,peterdettman/secp256k1,sipa/secp256k1-zkp,voisine/secp256k1,ElementsProject/secp256k1-zkp,libmetrocoin/secp256k1,Justaphf/BitcoinUnlimited,sipa/secp256k1,chfast/secp256k1,cddjr/BitcoinUnlimited,BTCfork/hardfork_prototype_1_mvf-bu,afk11/secp256k1,voisine/secp256k1,voisine/secp256k1,Bitcoin-com/BUcash,BTCfork/hardfork_prototype_1_mvf-bu,01BTC10/secp256k1,ChrisXin/secp256k1,marcusdiaz/BitcoinUnlimited,libbitcoin/secp256k1,libmetrocoin/secp256k1,martindale/secp256k1-zkp,randy-waterhouse/secp256k1,shea256/secp256k1-zkp,martindale/secp256k1-zkp,pmienk/secp256k1,instagibbs/secp256k1,Bitcoin-com/BUcash,libmetrocoin/secp256k1,ChrisXin/secp256k1,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,martindale/secp256k1-zkp,Bitcoin-com/BUcash,01BTC10/secp256k1,Justaphf/BitcoinUnlimited,evoskuil/secp256k1,GSongHashrate/secp256k1,BitcoinUnlimited/BitcoinUnlimited,apoelstra/secp256k1,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,voisine/secp256k1,bitcoin/secp256k1,rustyrussell/secp256k1,libbitcoin/secp256k1,kleetus/secp256k1,GSongHashrate/secp256k1,BitcoinUnlimited/BitcoinUnlimited,peterdettman/secp256k1,Justaphf/BitcoinUnlimited,sipa/secp256k1,marcusdiaz/BitcoinUnlimited,krzysztofwos/BitcoinUnlimited,krzysztofwos/BitcoinUnlimited,evoskuil/secp256k1,vlajos/secp256k1,cddjr/BitcoinUnlimited,krzysztofwos/BitcoinUnlimited,bitcoin/secp256k1,bitcoin/secp256k1,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,krzysztofwos/BitcoinUnlimited,Bitcoin-com/BUcash,vlajos/secp256k1,chfast/secp256k1,ChrisXin/secp256k1,Gustav-Simonsson/secp256k1,apoelstra/secp256k1,randy-waterhouse/secp256k1,Justaphf/BitcoinUnlimited,kleetus/secp256k1,BTCfork/hardfork_prototype_1_mvf-bu,instagibbs/secp256k1,randy-waterhouse/secp256k1,vlajos/secp256k1,01BTC10/secp256k1,Bitcoin-com/BUcash,Justaphf/BitcoinUnlimited,sipa/secp256k1-zkp,martindale/secp256k1,evoskuil/secp256k1,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,BitcoinUnlimited/BitcoinUnlimited,Gustav-Simonsson/secp256k1,kleetus/secp256k1,bitcoin/secp256k1,sipa/secp256k1-zkp,digitalbitbox/secp256k1,shea256/secp256k1-zkp,Gustav-Simonsson/secp256k1,GSongHashrate/secp256k1,vlajos/secp256k1,martindale/secp256k1,kleetus/secp256k1,shea256/secp256k1-zkp,chfast/secp256k1,bitcoin-core/secp256k1,evoskuil/secp256k1,cddjr/BitcoinUnlimited,digitalbitbox/secp256k1,BTCfork/hardfork_prototype_1_mvf-bu,afk11/secp256k1,voisine/secp256k1,marcusdiaz/BitcoinUnlimited,afk11/secp256k1,digitalbitbox/secp256k1,01BTC10/secp256k1,sipa/secp256k1-zkp,sipa/secp256k1,instagibbs/secp256k1,marcusdiaz/BitcoinUnlimited,pmienk/secp256k1,BitcoinUnlimited/BitcoinUnlimited,libbitcoin/secp256k1,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,cddjr/BitcoinUnlimited,digitalbitbox/secp256k1,pmienk/secp256k1,marcusdiaz/BitcoinUnlimited,cddjr/BitcoinUnlimited,sipa/secp256k1-zkp,martindale/secp256k1,Bitcoin-com/BUcash,chfast/secp256k1,evoskuil/secp256k1,pmienk/secp256k1,bitcoin/secp256k1,rustyrussell/secp256k1,GSongHashrate/secp256k1,randy-waterhouse/secp256k1,BitcoinUnlimited/BitcoinUnlimited,ElementsProject/secp256k1-zkp,martindale/secp256k1,libbitcoin/secp256k1,martindale/secp256k1-zkp,BitcoinUnlimited/BitcoinUnlimited,Justaphf/BitcoinUnlimited,krzysztofwos/BitcoinUnlimited,afk11/secp256k1