some build.scala improvements ported from an unsuccessful attempt at #295
some build.scala improvements ported from an unsuccessful attempt at #295

Dveim/scalameta,scalameta/scalameta,MasseGuillaume/scalameta,MasseGuillaume/scalameta,DavidDudson/scalameta,olafurpg/scalameta,scalameta/scalameta,DavidDudson/scalameta,scalameta/scalameta,olafurpg/scalameta,scalameta/scalameta,xeno-by/scalameta,scalameta/scalameta,olafurpg/scalameta,xeno-by/scalameta,MasseGuillaume/scalameta,xeno-by/scalameta