Eliminated a race condition in the threaded dslash
Added a new stream for the pthread build.
The interior dslash uses a lower priority stream than the packing, when
ensures that launching the interior dslash before packing does not delay
comms. Note we need to wait for the interior dslash to complete before
launching the exterior dslash kernels because they operate on the same fields.
Fixed compilation error due to Pthread support in non-pthread build.
Added cudaColorSpinorField::streamInit method
Added cudaColorSpinorField::pack methods that take a stream index as an argument
rather than a pointer.
Changed the threaded dslash so that both interior and exterior
dslash kernels are assigned to the same stream. This makes much more
sense logically since these kernels cannot run concurrently.
The packing kernel is now assigned to its own stream, which means
that packing and the interior dslash can execute concurrently.

Unfortunately, tuning is not currently working for the threaded dslash.
Merge remote branch 'origin/quda-0.7' into quda-0.7