Added message handles for the norm data used in the half-precision
Dslash, which will allow GPUDirect RDMA to be used in half precision.
Adding separate communication calls for the norms is
one way of getting around the fact that the norm data and field
data are not stored contiguously in cudaColorSpinorField, but it is not the
optimal approach. To enable efficient RDMA support we will need to store
the field and norm in a single array.
Implemented naive RDMA support for half-precision Dslash.
Moved the half-precision message handlers used in the GPU_COMMS build
from ColorSpinorField to cudaColorSpinorField. Added preprocessor
directive so handler pointers are only declared if GPU_COMMS is set.
Merge remote branch 'origin/quda-0.7' into quda-0.7
Fixed bug in half-precision dslash using GPU_COMMS.
Half precision now works when kernel packing in time is enabled.

Also updated staggered_dslash_test to use kernel packing in time
when GPU_COMMS is enabled. This should only be a temporary measure.
Merge remote branch 'origin/quda-0.7' into quda-0.7