When GTK3 is not found, HAVE_GTK was being set to TRUE. This edit
ensures that HAVE_GTK is only set if GTK3 or GTK2 (meeting minimum
version requirements) is present.
Selection logic for printing 'GTK: No' when the libraries are not found
has also been removed so the message is printed when GTK is not found or
selected in common with other libraries.

Changes committed:
	modified:   CMakeLists.txt
	modified:   cmake/OpenCVFindLibsGUI.cmake

The linux buildbots have started to fail compilation due to not
finding the gtk headers. The quotes have been changed to angle brackets
to indicate to the compiler that these are system includes.

During merging of conflicting versions of this file, I erroneously
deleted several lines in the GUI reporting section. This is repaired
in this commit.

Conflicts:
	CMakeLists.txt

Conflicts:

	modules/core/src/stat.cpp

Conflicts:
	modules/core/include/opencv2/core/version.hpp
	modules/core/src/out.cpp
	modules/cudaimgproc/test/test_hough.cpp
	modules/gpu/doc/introduction.rst
	modules/gpu/perf/perf_imgproc.cpp
	modules/gpu/src/generalized_hough.cpp
	modules/nonfree/perf/perf_main.cpp

Comment ipp version of CV_BGR2GRAY color convertion, by problems in BRIEF accuracy test and Path_Idx_Cn_NPoints_WSize perfomance test

Enable ipp MeanStdDev calculation for 32F_C1 images. Decrease accuracy sanity check of the perfomance test

Canny uncommented, prefix of ipp function changed. Ipp version of Canny called only for images with one channels