Thrust library issues

At some later time we might want to move to a newer version of the thrust library. Note that if we move to a version past 1.3, the gather routines will change their interface which will affect the codes in include/comm/detail -- don't forget to change the thrust::gather calls to reflect the change of interface (in version 1.2 the thrust::gather routines don't exist -- they are replaced with thrust::deprecated::gather for the old interfaces and thrust::next::gather for the new ones).

Note that this issue is now fixed: we have moved to the new thrust library.