TST: Fix ValueError: Buffer dtype mismatch, expected 'intp_t' but got...

...'long'

```
======================================================================
ERROR: test_hough_transform.test_hough_circle
----------------------------------------------------------------------
Traceback (most recent call last):
  File "X:\Python33\lib\site-packages\nose\case.py", line 198, in runTest
    self.test(*self.arg)
  File "X:\Python33\lib\site-packages\skimage\transform\tests\test_hough_transform.py", line 125, in test_hough_circle
    out = tf.hough_circle(img, np.array([radius]))
  File "_hough_transform.pyx", line 23, in skimage.transform._hough_transform.hough_circle (skimage\transform\_hough_transform.c:2286)
ValueError: Buffer dtype mismatch, expected 'intp_t' but got 'long'

======================================================================
ERROR: test_hough_transform.test_hough_circle_extended
----------------------------------------------------------------------
Traceback (most recent call last):
  File "X:\Python33\lib\site-packages\nose\case.py", line 198, in runTest
    self.test(*self.arg)
  File "X:\Python33\lib\site-packages\skimage\transform\tests\test_hough_transform.py", line 141, in test_hough_circle_extended
    out = tf.hough_circle(img, np.array([radius]), full_output=True)
  File "_hough_transform.pyx", line 23, in skimage.transform._hough_transform.hough_circle (skimage\transform\_hough_transform.c:2286)
ValueError: Buffer dtype mismatch, expected 'intp_t' but got 'long'
```