Fix computeBoundingBox/Sphere for relative morph targets
Fix computeBoundingBox/Sphere for relative morph targets

expandByVector is not correct to call here; if a morph target has a min
of [1,1,1], it should *not* change the box.min but it should expand
box.max by 1.

To avoid doing per-component math we use addVectors to get the corners
of the box, and use expandByPoint to union the box with the resulting
point.

SpinVR/three.js,QingchaoHu/three.js,SpinVR/three.js,fraguada/three.js,kaisalmen/three.js,TristanVALCKE/three.js,QingchaoHu/three.js,fraguada/three.js,Liuer/three.js,TristanVALCKE/three.js,Samsy/three.js,zhoushijie163/three.js,fraguada/three.js,TristanVALCKE/three.js,WestLangley/three.js,greggman/three.js,kaisalmen/three.js,makc/three.js.fork,makc/three.js.fork,stanford-gfx/three.js,Samsy/three.js,06wj/three.js,mrdoob/three.js,06wj/three.js,fyoudine/three.js,aardgoose/three.js,gero3/three.js,looeee/three.js,Itee/three.js,fraguada/three.js,Samsy/three.js,mrdoob/three.js,donmccurdy/three.js,aardgoose/three.js,Samsy/three.js,TristanVALCKE/three.js,WestLangley/three.js,fraguada/three.js,fyoudine/three.js,donmccurdy/three.js,gero3/three.js,fraguada/three.js,TristanVALCKE/three.js,stanford-gfx/three.js,Samsy/three.js,jpweeks/three.js,zhoushijie163/three.js,looeee/three.js,Samsy/three.js,Liuer/three.js,jpweeks/three.js,greggman/three.js,TristanVALCKE/three.js,Itee/three.js