Replaced __device__ and __host__ with define

 - resides in new file "policy_malloc_prefixes.hpp"
 - not in the policies that are CUDA-specific (it is better to get the
   compile-error from a non-cuda compiler, I suppose)
add macro providesAvailableSlots
minor fix
Merge pull request #47 from slizzered/replace_explicit_device_prefixes

Replace explicit device prefixes