[Bf-python] Layer setting problem

[Campbell Barton]

At the moment ob1.Layers = ob2.Layers can raise an error if ob1 is in 
localView
the simple solution is to mask off the last 8 bits when getting the 
layers, but this means a script running in Local view cant creat a new 
oject in that local view.

Would an acceptable solution be to allow local view bits to be set by doing
ob.Layer =  layer & (G.vd->lay & 1<<21-1)

The bad thing about this is that it assumes that the object is in the 
current scene. it could be bad for objects in other scenes however the 
worst thing is local bits will be set.