Warnings fix;

e.g. <opencv2/core/core.hpp> become <opencv2/core.hpp>

Also renamed <opencv2/core/opengl_interop.hpp> to <opencv2/core/opengl.hpp>

Made all STL usages explicit to be able automatically find all usages of
particular class or function.

test code unified - channels number is tested for other formats as well

* fixed indentation to use spaces and trailing spaces

Added test checking that all valid fourcc values are converted properly

Сonflict exists between some versions of libtiff and opencv headers

OpenCV issue #2604

After this patch applied an attempt to encode empty images produces exception
saying "Raw image encoder error: Empty JPEG image (DNL not supported)"

This reverts commit 2e7656db.

disabled several tests on Mac when no FFMPEG is used; disabled automatic table initialization in imgwarp in the case of MinGW