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. 

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57203 954f8c5b-7b00-dc11-b283-0030488c597c