Front/back camera constants semantic for Android fixed (Bug #2839).

Front/Back camera constants' values changed;
Additional camera facing check added for JavaCameraView.
make boxfilter kernel compile on Mac GPU OCL
Add OclCascadeClassifierBuf interface
fixing build and lint warnings
Add OpenCL stereo CSBP implementation
Fix build errors
Fix a bug found on Intel OpenCL SDK.
use float when sum overflow
Fix thread sync for csbp.
fix a crash on CPU OCL for some specified image sizes
Front/Back camera semantic support added to Android VideoCapture back-end.
Fix android tutorial 3 second picture taken bug
Calib3d documentation:
- fixed reference to Slabaugh
Changed convexHull's documentation to essentially invert the meaning of ``clockwise``.

The orientation of convexHull's result is currently the opposite of what the
documentation would suggest:

>>> import cv2, numpy as np
>>> points = np.array([[0,0],[0,1],[1,0]], dtype=np.int32)
>>> cv2.convexHull(points, clockwise=False)
array([[[1, 0]],
       [[0, 1]],
       [[0, 0]]], dtype=int32)
>>> cv2.convexHull(points, clockwise=True)
array([[[0, 0]],
       [[0, 1]],
       [[1, 0]]], dtype=int32)

Changing the function itself is probably not a good idea at this point, so
this fixes the documentation by flipping the coordinate system.

I also removed the mention of the origin, since it's irrelevant for this
function.
Merge pull request #843 from pengx17:2.4_stereobp_fix
Merge pull request #844 from bitwangyaoyao:2.4_integral
Merge pull request #827 from apavlenko:fix_android_tutorial1
Merge pull request #800 from asmorkalov:android_cam_idx_semantic
NullPointerException in case of error on opening native camera fixed.
fixing precommit build on ubuntu-64 (now it takes OCL headers from non-default OCL SDK, but libs from default one)