Warn about @2x and @3x resources that aren’t that multiple

[David Dunham]

My artist delivered an @2x asset which is 255 * 191 px. Without looking at any other resources, this is clearly incorrect. (It would not be a valid @3x asset either…)

(I vaguely remember getting errors like this, but it was ~4 years ago and might have been a different tool than Faux Pas?)