Merge pull request #12674 from dmatveev:gapi_upd270918

* Update G-API code base to 27-Sep-18

Changes mostly improve standalone build support

* G-API code base update 28-09-2018

* Windows/Documentation warnings should be fixed
* Fixed stability issues in Fluid backend
* Fixed precompiled headers issues in G-API source files

* G-API code base update 28-09-18 EOD

* Fixed several static analysis issues
* Fixed issues found when G-API is built in a standalone mode

modules/gapi/src/api/gkernel.cpp

@@ -5,13 +5,13 @@
 // Copyright (C) 2018 Intel Corporation
 
 
+#include "precomp.hpp"
 #include <iostream> // cerr
 #include <functional> // hash
 #include <numeric> // accumulate
 
 #include <ade/util/algorithm.hpp>
 
-#include "opencv2/core/cvdef.h"
 #include "logger.hpp"
 #include "opencv2/gapi/gkernel.hpp"