BUG: fix buffer dtype mismatch on win-amd64

Using scipy-0.15.0b1.win-amd64-py3.4:
```
======================================================================
ERROR: test_mls_inputs (test_max_len_seq.TestMLS)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "X:\Python34\lib\site-packages\scipy\signal\tests\test_max_len_seq.py", line 22, in test_mls_inputs
    assert_array_equal(max_len_seq(10, length=0)[0], [])
  File "scipy\signal\_max_len_seq.pyx", line 104, in scipy.signal._max_len_seq.max_len_seq (scipy\signal\_max_len_seq.c:2172)
ValueError: Buffer dtype mismatch, expected 'Py_ssize_t' but got 'long'

======================================================================
ERROR: test_mls_output (test_max_len_seq.TestMLS)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "X:\Python34\lib\site-packages\scipy\signal\tests\test_max_len_seq.py", line 39, in test_mls_output
    taps=taps)[0]
  File "scipy\signal\_max_len_seq.pyx", line 104, in scipy.signal._max_len_seq.max_len_seq (scipy\signal\_max_len_seq.c:2172)
ValueError: Buffer dtype mismatch, expected 'Py_ssize_t' but got 'long'
```