Merge #21: elip200: fix discount weight calculation for asset and nonce

9f08b81 elip200: fix discount weight calculation for asset and nonce (Byron Hambly)

Pull request description:

  output amount and nonce discount must be weighted by the witness scaling factor as they form part of the base transaction, not the witness data

  see ElementsProject/elements#1366 and ElementsProject/rust-elements#218

ACKs for top commit:
  apoelstra:
    ACK 9f08b81

Tree-SHA512: c719cd0343887d11b28037cb1b15da73b9d139f95a8c75bb91dd8ea126ed8cf8781485dd6ef26304adb8cd1a08b60c4ee0a14480f25619950f67a1d394d64e3e