Arithmetic overflow when passing large integer range to RNG

[mattwala]

Running this snippet results in the following error:

File "test.py", line 11, in <module>
  rand(q, shape=(), a=np.iinfo(dt).min, b=np.iinfo(dt).max, dtype=dt)
File "/home/matt/src/pyopencl/pyopencl/clrandom.py", line 741, in rand
  gen.fill_uniform(result, a=a, b=b))
File "/home/matt/src/pyopencl/pyopencl/clrandom.py", line 651, in fill_uniform
  scale=(b-a), shift=a, queue=queue)
File "/home/matt/src/pyopencl/pyopencl/clrandom.py", line 638, in _fill
  evt = knl(queue, gsize, lsize, *args)
File "/home/matt/src/pyopencl/pyopencl/cffi_cl.py", line 1964, in __call__
  return self._enqueue(self, queue, global_size, local_size, *args, **kwargs)
File "<generated function enqueue_knl_generate>", line 81, in enqueue_knl_generate
struct.error: 'i' format requires -2147483648 <= number <= 2147483647

This is probably due to the fact that b-a is out of range.