Save selected FCC in order to return proper CV_CAP_PROP_FOURCC property value (currently FCC for RGB24 is always returned).

FOURCC code bytes should be placed in the reverse order.

Set correct value of sample size when calling IAMStreamConfig::SetFormat function. For non-RGB media type it can be set to zero value.
(See http://msdn.microsoft.com/en-us/library/windows/desktop/dd373477%28v=vs.85%29.aspx)

Use _com_ptr_t instead of CComPtr in ComPtr wrapper to avoid ATL dependency.

The Mutex manager registered with ffmpeg must reset the mutex to NULL after destruction, otherwise ffmpeg will give the invalid mutex to the next mutex manager when it asks it to CREATE a new mutex.
See ffmpeg code: http://git.videolan.org/?p=ffmpeg.git;a=blob;f=libavcodec/utils.c;h=28c5785398fcf11a3d3c70a8cd09e9df798e2734;hb=HEAD#l3423

Cherry picked from head (file has moved but issue is the same).
Conflicts:
	modules/videoio/src/cap_ffmpeg_impl.hpp

Currently, FFMPEG source files are included in highgui project file regardless of CMake WITH_FFMPEG option.
After applying this PR FFMPEG files are included only if WITH_FFMPEG option is enabled.

Taken from 3f076552