Merge 2.4 into master

Original pull requests:

* #1590 from ilya-lavrenov:cmd_parser_fix
* #1744 from liuxing6666:2.4_fix_harris_test
* #1797 from moodoki:bugfix_3344
* #1845 from StevenPuttemans:bugfix_3306
* #1849 from StevenPuttemans:feature_3375_documentation
* #1856 from alalek:ocl_fix_mt
* #1858 from StevenPuttemans:updates_traincascade
* #1873 from abak:hough_24
* #1875 from asmorkalov:android_bin_compat_fix
* #1877 from tim36272:patch-2
* #1879 from LeszekSwirski:traincascade-2.4
* #1884 from asmorkalov:winrt_img_proc_sample
* #1885 from jet47:gpu-bgfg-test-fix
* #1887 from jet47:android-cuda-6.0
* #1892 from asmorkalov:android_native_camera_close_fix
* #1894 from asmorkalov:ocv_debug_build
* #1897 from berak:b_3393_24
* #1898 from berak:b_3349_24
* #1899 from berak:b_3171_24
* #1906 from asmorkalov:android_ocl_warn_fix