interpolation: OpenCL implementation of interpolation_resample

implementation with naive 1:1 copy of CPU code. as to be expected this is
slow as hell combined with a huge workload on the gpu
Merge branch 'master' into interpolation
Merge branch 'master' into interpolation
opencl, interpolation: a bit less naive implementation
opencl, interpolation: make better use of local memory

speed wise this should now be ahead of the CPU code
opencl, interpolation: small fix and some added comments
opencl, interpolation: catch cases where the GPU code cannot process efficiently: fall back to CPU
Merge pull request #468 from upegelow/interpolation

OpenCL implementation of pixel interpolator