Change iteration to iterate separately when the video is decode on a GPU to account for different number of frames

Update hog.cpp (#12649)

- avoid memory access violation during "prefetch" stage

This commit fixes an issue while trying to compile
on s390x architecture.

This is simply a backport of a fixe already applied
in official protobuf code:
- https://github.com/protocolbuffers/protobuf/pull/3955

TS: fix Python v2/v3 compatibility (#12667)

* TS: fix Python2.7 compatibility

* TS: fix Python3 compatibility

* py3: use integer division '/' => '//' instead of cast

  especially if it matches the module being tested

  * follow the implementation of Luv2RGBfloat in imgproc/src/color_lab.cpp
  * loosen threshold in cudaimgproc

'mFramesCouner' -> 'mFramesCounter'

* hide use of std::mutex from /clr compilation under Visual Studio

C++11 <mutex> is not available when compiling with  /clr under Visual Studio, thus opencv cannot be easily included.
It is fixed by making a CEEMutex wrapper class, around an opaque implementation using std::mutex internally

* fixed compilation outside of Visual Studio

fixed compilation outside of Visual Studio by avoiding some macros

* fixed indentation, prepare getting rid of CEEMutex/CEELockGuard

fixed indentation
After discussion, CEEMutex and CEELockGuard can be totally removed, letting the developer in a /clr context to provide his own implementation

* remove CEEMutex/CEELockGuard

* 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