Using Runge-Kutta 2nd order in test/generator.cpp
Using Runge-Kutta 2nd order in test/generator.cpp

4th order method resulted in a kernel with too many parameters
which lead to segfault on AMD OpenCL.

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