Altered viennacl custom operations

Version 1.4.0-preview of viennacl requires kernel name parameter for custom
operations.
Removed tabs
Removed const_cast from viennacl operations

This is not required in the latest version
viennacl use default operations unless VIENNACL_WITH_OPENCL is defined
Merge pull request #52 from ddemidov/master

Changes in viennacl_operations for ViennaCL-1.4.0-preview