added compute function to Feature2D (dirty workaround for #2699)
Fix for spurious assert in cv::compareHist

When comparing histograms that look like multi-channel images (e.g a 3D histogram, of 4x4x4 bins, might appear as a CV_32FC4 matrix), cv::compareHist would complain because it was expecting the matrix type() == CV_32F. Now we test matrix depth() == CV_32F instead.
libd1394 2.x support for mingw on windows added
libd1394 2.x support for mingw on windows added
Merge branch 'mingw-libdc1394-2-windows' of https://github.com/dominikrose/opencv into mingw-libdc1394-2-windows
Merge branch 'mingw-libdc1394-2-windows' of https://github.com/dominikrose/opencv into mingw-libdc1394-2-windows
Merge branch 'mingw-libdc1394-2-windows' of https://github.com/dominikrose/opencv into mingw-libdc1394-2-windows
Merge branch 'mingw-libdc1394-2-windows' of https://github.com/dominikrose/opencv into mingw-libdc1394-2-windows
Merge branch 'mingw-libdc1394-2-windows' of https://github.com/dominikrose/opencv into mingw-libdc1394-2-windows
libdc1394 - removed validation for msvc compiler in CMakeLists.txt
Take account of multi-channel matrices when comparing histograms

Ensure that all channels are considered when comparing multi-channel histograms
Bug #2967, basic_structures.rst, fix 2 typos
Bug #2967, void DescriptorMatcher::radiusMatch() // description unclear,
only file:  common_interfaces_of_descriptor_matchers.rst
Bug #2966, insert CV_Assert(size.width>0 && size.height>0); in imshow()
Fix drawing documentation referring to C API macros
(tab to space) 2x
(typo)
[3rd attempt] fixed HOGDescriptor::detectMultiScale() to group weights as well as ROIs
Add ocl's good features to track implementation.
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.
Fixed include name in OpenCL on OS X