opencv: Change configure test to check for OpenCV2 headers

* Checks for opencv2 headers only, not for legacy opencv1 headers
* Checks for every opencv2 header that the implementation needs,
  not just highgui_c.h

https://bugzilla.gnome.org/show_bug.cgi?id=725163

configure.ac

@@ -2447,15 +2447,26 @@ AG_GST_CHECK_FEATURE(OPENCV, [opencv plugins], opencv, [
     AC_LANG([C++])
     OLD_CPPFLAGS=$CPPFLAGS
     CPPFLAGS=$OPENCV_CFLAGS
-    AC_CHECK_HEADERS([highgui.h opencv2/highgui/highgui_c.h])
+    something_not_found=no
+    AC_CHECK_HEADERS([opencv2/contrib/contrib.hpp \
+                      opencv2/core/core_c.h \
+                      opencv2/core/types_c.h \
+                      opencv2/core/version.hpp \
+                      opencv2/highgui/highgui_c.h \
+                      opencv2/imgproc/imgproc.hpp \
+                      opencv2/imgproc/imgproc_c.h \
+                      opencv2/legacy/compat.hpp \
+                      opencv2/legacy/legacy.hpp \
+                      opencv2/objdetect/objdetect.hpp \
+                      opencv2/video/background_segm.hpp], [], [something_not_found=yes])
     CPPFLAGS=$OLD_CPPFLAGS
     AC_LANG([C])
 
-    if test $ac_cv_header_highgui_h = "yes" -o $ac_cv_header_opencv2_highgui_highgui_c_h = "yes" ; then
-      HAVE_OPENCV="yes"
-    else
-      AC_MSG_RESULT([neither highgui.h nor opencv2/highgui/highgui_c.h could not be found])
+    if test $something_not_found = "yes"; then
+      AC_MSG_RESULT([not all opencv2 headers were found])
       HAVE_OPENCV="no"
+    else
+      HAVE_OPENCV="yes"
     fi
   ], [
     HAVE_OPENCV="no"