Convert numpy int64s to ints before calling PyCUDA
Merge pull request #229 from OP2/cuda-firedrake-fix

Fix for using Firedrake with CUDA

nblock and the size of datasets seem to be `numpy.int64` types when
running with Firedrake.

This commit converts them to `int` before passing them to PyCUDA. 

The Firedrake tests can pass with the CUDA backend, with the following
exceptions:

* The identity test for degrees 3 and 4 is problematic because it makes
  cicc (part of the CUDA compiler) go into a slow loop consuming 100%
  CPU. It eventually finished compiling for degree 3 after about 10
  minutes but I didn't wait for the degree 4 case to finish compiling. 
* The firedrake_identity_parallel test fails as expected (uses MPI).