Fix the following error for ocl::getOpenCLPlatforms() on Ubuntu 12.04 with gcc 4.8
OpenCV Error: Unknown error code -6 (OpenCL function is not available: [clGetPlatformIDs]) in opencl_check_fn, file /home/ahb/software/opencv/modules/ocl/src/cl_runtime/cl_runtime.cpp, line 83

The issue results from modules/ocl/src/cl_runtime/cl_runtime.cpp checking for
"linux" instead of "__linux__" (cp.  http://sourceforge.net/p/predef/wiki/OperatingSystems/)

Adjust all other occurrences of "defined(linux)" as well.
Merge pull request #2133 from apavlenko:2.4-perf_haar
deleted extra arg in case of power=0.5
Merge branch 'master' of https://github.com/Itseez/opencv into brief_cl
Merge pull request #2147 from ilya-lavrenov:tapi_sqrt
Merge remote-tracking branch 'origin/2.4' into merge-2.4

Conflicts:
	modules/contrib/src/retina.cpp
	modules/core/include/opencv2/core/mat.hpp
	modules/core/src/algorithm.cpp
	modules/core/src/arithm.cpp
	modules/features2d/src/features2d_init.cpp
	modules/gpu/include/opencv2/gpu/gpu.hpp
	modules/gpu/perf/perf_imgproc.cpp
	modules/imgproc/src/generalized_hough.cpp
	modules/ocl/include/opencv2/ocl/ocl.hpp
	modules/video/src/tvl1flow.cpp
	modules/video/src/video_init.cpp
Merge pull request #2145 from andreasBihlmaier:2.4
Added PVAPI enums to highgui.hpp
Added "PVAPI_" prefix to FrameStartTriggerMode definition
fixed cv::cvtColor
fixing compilation if `WITH_OPENCL=OFF`
adding old cascade
Small fix for extracting mouse coordinates on Windows, in a way that will always work with multiple monitors.
This is the way recommended by Microsoft.
Added support for mouse-wheel events on Windows.
To be used in the mouse callback like this:
    if (CV_EVENT_MOUSEWHEEL == CV_GET_MOUSEWHEEL_EVENT(event))
    {
       int delta= CV_GET_WHEEL_DELTA(event);
       // use delta...
    }
[HighGUI] Updated mouse wheel delta to reside within the 'flags' variable. Updated C++ API.
fixing bug #3345. don't use BORDER_ISOLATED alone. it should be combined with some border type
Merge pull request #2150 from ilya-lavrenov:tapi_cvtcolor
changed testdata path for calib3d
added perf test for cv::Canny
Added optional constraints to non-probablistic hough lines functions
Merge pull request #2127 from apavlenko:perf_cascades