This removes the option from the wallet to not pay a fee on "small"
transactions which spend "old" inputs.
This code is no longer worth keeping around, as almost all miners
prefer not to include transactions which pay no fee at all.
$ contrib/devtools/copyright_header.py update .
Amended by Pieter Wuille to use multisig 1-of-1 for P2WSH tests, and BIP9
based switchover logic.
Fixes and py3 conversion by Marco Falke.