If-condition was always true (alpha = 0.5 is set in Line 19).
Now the user input is checked to be between 0 and 1.
This is correct in the tutorial code for OpenCV 2.4.

* fix typos.

* Fix typos.

* Fix typos.

* Fix typos.

* Fix typos.

Now a user can use `std::cout` to print an object of `cv::UMat` just like `cv::Mat`.

* Fix the documentation for Mat::diag(int).

Fix issue #8181

* Fix the documentation for Mat::diag(int).

Fix issue #8181.

* Add support for printing out cv::Complex.

* Remove extra spaces.

* cv::Complex is submitted as a new pull request.

Instead of CL_DEVICE_EXTENSIONS in Querying OpenCLVersion, it should be CL_DEVICE_VERSION flag which needs to be passed to the function.

Add support for printing out cv::Complex. (#8208)

* Add support for printing out cv::Complex.

* Conform to the format of std::complex.

* Remove extra spaces.

* Remove extra spaces.

Although both `cl_platform_info` and `cl_device_info` are defined as macro `cl_uint`, it needs to use `cl_platform_info` to get
the platform information.

- don't use undefined flag=0. It should be CONSTANT instead.
- don't allow 'UMat* m=NULL' argument (except LOCAL/CONSTANT flags).
  This case is not handled well to provide NULL __global pointers.
  It is better to use '-D' macro defines instead (at least for performance)