Add run test for type ctypedef and PyType_IsSubtype.

tests/run/pytype.pyx

+from cpython.type cimport PyType_IsSubtype
+
+class mylist(list): pass
+
+def test_issubtype(a, b):
+    """
+    >>> test_issubtype(mylist, list)
+    True
+    >>> test_issubtype(mylist, dict)
+    False
+
+    >>> o = object()
+    >>> test_issubtype(o, list)
+    Traceback (most recent call last):
+    ...
+    TypeError: Cannot convert object to type
+    """
+    return PyType_IsSubtype(a, b)