Cycles / Math functions:

* Rename some math functions:
len -> length
len_squared -> length_squared
normalize_len -> normalize_length

* This way OpenCL uses its inbuilt length() function, rather than our own. The other two functions have been renamed for consistency. 
* Tested CPU, CUDA and OpenCL compile, should be no functional changes.

intern/cycles/render/mesh.cpp

@@ -187,7 +187,7 @@ void Mesh::add_face_normals()
 			float3 v2 = verts_ptr[t.v[2]];
 
 			float3 norm = cross(v1 - v0, v2 - v0);
-			float normlen = len(norm);
+			float normlen = length(norm);
 			if(normlen == 0.0f)
 				fN[i] = make_float3(0.0f, 0.0f, 0.0f);
 			else