Added few opencl optimizations (as Intel platform codepath):

1. HaarDetetctor: repack nodes to reduce memory footprint
2. cornerMinEigVal: 4 ocl kernels are fused into 1 for sobel calculation
try to fix build error
try to made compatible with mac
rename imageproc_sobel2.cl -> imageproc_sobel3.cl for consistency
fix bugs on host and device sides for imgprog_sobel3.cl
Merge pull request #1675 from krodyush:opencl-optimization