specific code. As a result of this, HAVE_GTK3 no longer needs to be
exposed.
The use of HAVE_GTK, and HAVE_ GTK3 have been changed to mirror the
method used by HAVE_QT and HAVE_QT5.
On branch gtk3
Changes to be committed:
modified: CMakeLists.txt
modified: cmake/OpenCVFindLibsGUI.cmake
modified: cmake/templates/cvconfig.h.in
modified: modules/highgui/src/window.cpp
modified: modules/highgui/src/window_gtk.cpp
7f671406db