introducing a tutorial for the retina model
adding retina tutorial
updated tutorial, need spell check, validation, nicer images and a discussion on parameters
updated tutorial, rapid spell check, retina parameters discussion added
added retina code tutorial
updated first image sample
minor update
minor updates for doc redirections and tutorial images size
Super Resolution module
fix mismatch on NV OCL and some AMD GPUs
Stetch support for Android View classes added (Feature #2840)
add stereoBM function
remove the OpenCL define
Add ocl::SURF accurate test.

The test cases are ported from gpu module (masked version is still
missing).
Key point direction definition is synchronized with cv::SURF.
nonfree module dependency is added into ocl module's cmake file.
gpu : implement Bayer* -> Gray color conversion
Merge pull request #630 from asmorkalov:android_view_stretch
Merge pull request #633 from jet47:gpu-debayer-gray
fix warnings on Linux
Remove unnecessary HAVE_OPENCL macro block.
Fix a bug in ocl::Erode/Dilate, simplify the host logic