Add documentation.

Most codes are ported from AMD's Bolt library.
Four methods are implemented:

SORT_BITONIC,   // only support power-of-2 buffer size
SORT_SELECTION, // cannot sort duplicate keys
SORT_MERGE,
SORT_RADIX      // only support signed int/float keys

Revise some descriptions of the enums.

Test cases (accuracy and performance) are provided.

Previously the feature is controlled by setBinpath implicitly.
We add the function to cope with setBinpath and setBinpath is only
useful when setBinaryDiskCache is set.
Refer to the header to see more info.

On a Mac with a case sensitive filesystem <OpenCL/OpenCL.h> does not exist but <OpenCL/opencl.h> does. I presume (!), but have no way to test, that on a Mac with case insensitive FS this change will make no difference.

In current implementation, this function only works when anchor point is
in the kernel center and kernel size supported is either 3x3 or 5x5.

For example, haarcascade_frontalface_alt2.xml is now supported.
Note that classifier's pattern of a cascade file must be consistent,
i.e., all trees must either have two nodes or one node, otherwise
unexpected results will occur.

Other fixes:
Test cases are updated.
Some unused codes are removed.
Fix some problems of haar when using OclCascadeClassifierBuf.

Additional notes with this commit:
1. Add cornerHarris_dxdy and cornerMinEigenVal_dxdy to get
the interim dx and dy output of Sobel operator;
2. Add minMax_buf to allow user to reuse buffers in minMax;
3. Fix an error when either min or max pointer fed into minMax is NULL;
4. Corner sorter temporarily uses C++ STL's quick sort. A parallel
 selection sort in OpneCL is contained in the implementation but disabled
due to poor performance at the moment.
5. Accuracy test for ocl gfft.

This adds a similar interface with pure-cpp and gpu versions.

Affected functions surf.ocl, pyrlk.ocl and hog.ocl are updated with the change.

Previously the function may cause some unsafe issue. It is fixed now by introducing a template parameter.

Add backwards portability for OpenCL 1.1 when OpenCV executables
are compiled with OpenCL 1.2 profile support.