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/subd/subd_split.cpp

@@ -74,7 +74,7 @@ int DiagSplit::T(Patch *patch, float2 Pstart, float2 Pend)
 		float3 P = project(patch, Pstart + t*(Pend - Pstart));
 
 		if(i > 0) {
-			float L = len(P - Plast);
+			float L = length(P - Plast);
 			Lsum += L;
 			Lmax = max(L, Lmax);
 		}