Revert "create callback differently on julia v0.2"
Revert "create callback differently on julia v0.2"

This reverts commit 67e3332545918a258e8df7fea395afb2c2220222.

tkelman/OpenCL.jl,tkelman/OpenCL.jl,JuliaPackageMirrors/OpenCL.jl,yuyichao/OpenCL.jl,JuliaPackageMirrors/OpenCL.jl,yuyichao/OpenCL.jl