Made canBeReplacedByLeaves default to whether a block isn't opaque rather than if it is, also uninverted the checks for canBeReplacedByLeaves in WorldGenBigMushroom, WorldGenSwamp, WorldGenTaiga1 and WorldGenTaiga2
Merge pull request #915 from Adubbz/master

Made canBeReplacedByLeaves default to whether a block isn't opaque rathe...