make truffle compile stop altering artifact files whose contracts have not changed

[dkent600]

Apparently every time we compile the contracts, truffle compile alters the artifact files even for contracts that have not changed.

This adds risk for us because we are pushing altered artifact files even though the changes have no relation to the contract changes that we have made, and without understanding the nature of these surprise changes.

So I propose that we undertake to understand the nature of these surprise changes, and try to configure truffle compile not to make them.