Better check for broken NumPy install

tests/run/numpy_test.pyx

@@ -17,6 +17,8 @@ try:
     import numpy as np
     __doc__ = u"""
 
+    >>> assert_dtype_sizes()
+
     >>> basic()
     [[0 1 2 3 4]
      [5 6 7 8 9]]
@@ -209,6 +211,20 @@ except:
     __doc__ = u""
 
 
+def assert_dtype_sizes():
+    assert sizeof(np.int8_t) == 1
+    assert sizeof(np.int16_t) == 2
+    assert sizeof(np.int32_t) == 4
+    assert sizeof(np.int64_t) == 8
+    assert sizeof(np.uint8_t) == 1
+    assert sizeof(np.uint16_t) == 2
+    assert sizeof(np.uint32_t) == 4
+    assert sizeof(np.uint64_t) == 8
+    assert sizeof(np.float32_t) == 4
+    assert sizeof(np.float64_t) == 8
+    assert sizeof(np.complex64_t) == 8
+    assert sizeof(np.complex128_t) == 16
+
 def ndarray_str(arr):
     u"""
     Since Py2.3 doctest don't support <BLANKLINE>, manually replace blank lines