NetBSD video(4) support, patch 2 of 3

* Decouple Video4Linux2 support from Video4Linux as existence of
  v4l2 on a system does not imply support for v4l.
* Don't use V4L's struct video_window in V4L2 code.
* Removed __USE_GNU as comment says:
      /* support for MJPEG is only available with libjpeg and gcc,
         because it's use libjepg and fmemopen()
  so replace with test for fmemopen() if found necessary.

modules/highgui/src/cap.cpp

@@ -172,7 +172,8 @@ CV_IMPL CvCapture * cvCreateCameraCapture (int index)
     defined(HAVE_TYZX)         || \
     defined(HAVE_VFW)          || \
     defined(HAVE_LIBV4L)       || \
-    (defined(HAVE_CAMV4L) && defined(HAVE_CAMV4L2)) || \
+    defined(HAVE_CAMV4L)       || \
+    defined(HAVE_CAMV4L2)      || \
     defined(HAVE_VIDEOIO)      || \
     defined(HAVE_GSTREAMER)    || \
     defined(HAVE_DC1394_2)     || \
@@ -217,7 +218,7 @@ CV_IMPL CvCapture * cvCreateCameraCapture (int index)
                 return capture;
 #endif
 
-#if defined HAVE_LIBV4L || (defined (HAVE_CAMV4L) && defined (HAVE_CAMV4L2)) || defined HAVE_VIDEOIO
+#if defined HAVE_LIBV4L || defined HAVE_CAMV4L || defined HAVE_CAMV4L2 || defined HAVE_VIDEOIO
             capture = cvCreateCameraCapture_V4L (index);
             if (capture)
                 return capture;