Make settxfee clear that units are btc/kb.
Make settxfee clear that units are btc/kb.

Rebased-from: fffab7e45061aba3a5f345e0fc22a8584bcb012d 0.8.x

MidasPaymentLTD/midascoin,MidasPaymentLTD/midascoin,MidasPaymentLTD/midascoin,MidasPaymentLTD/midascoin,MidasPaymentLTD/midascoin