Rewrite reduce_by_key test
Rewrite reduce_by_key test

So that VS2010 is able to compile it in Debug mode

ddemidov/vexcl,Poulpy21/vexcl,kapadia/vexcl,ddemidov/vexcl,kapadia/vexcl,Poulpy21/vexcl,Poulpy21/vexcl