fix unit tests for new math constructors that don't copy the parameters.
add initial Line3.js with unit tests.
Merge branch 'dev' of git@github.com:mrdoob/three.js.git into math-line
fix bug in Line3.distance/distanceSq
incorporate Line3 into Plane.
minor fixes to Line3, removing debug info.
add option to clamp to line or to just get closest point on infinite line.
add ability to get closestPointToPointParameter on a line.
(Box3|Line3|Plane|Ray|Sphere).transform() -> applyMatrix4() for consistency.
add THREE.Math.smoothStep and THREE.Math.smootherStep based on Wikipedia article.
test of Line3 -> LineSegment.
Rename back LineSegment to Line3 per @mrdoob's preference.
Merge remote-tracking branch 'bhouston/math-line' into dev