We're using elements.set() anyway...

THREE.extend improvements: adopt safe {}.hasOwnProperty method source.  Optimize Object.keys() based on @paulmillr suggestion.

Signed-off-by: NBen Houston <ben@exocortex.com>

fix three missed conversions to closures.  switch to extending math prototypes rather than replacing them.  This is to ensure that types created in closures within a type's prototype definition get their prototype updated with the full definition.

Added shadow map type definitions and replaced shadowMapSoft boolean on the renderer with shadowMapType. The default type is THREE.PCFShadowMap, which amounts to the previous default of shadowMapSoft = true. A new type, THREE.PCFSoftShadowMap will enable bilinear filtering of the shadow in the shader for smoother results.

These replace frontFaceDirection parameter strings in renderer.setFaceCulling( cullFace, frontFaceDirection ):

"cw"  => THREE.FrontFaceDirectionCW
"ccw" => THREE.FrontFaceDirectionCCW

See related cullFace constants changes in #2683

Default value THREE.CullFaceFront, other valid value THREE.CullFaceBack.

These constants also go into renderer.setFaceCulling( cullFace, frontFace ) where they replace strings:

"back"  => THREE.CullFaceBack
"front" => THREE.CullFaceFront
"frontback"    => THREE.CullFaceFrontBack
""/0/undefined => THREE.CullFaceNone

See discussion in #2683

Added "AddOperation" environment mapping combine type for additive cube maps reflections / refractions.

Fixes #2559

We'll see, if this becomes a bottleneck in the fragment shader, all three environment mapping combine options could be changed from uniforms & ifs into #ifdefs.