Bug#940679: pandas: random test crashes

[Rebecca N. Palmer]

Control: tags -1 - patch

That's not the problem: cdef classes _can_ have non-cdef class (not 
instance) attributes. https://github.com/cython/cython/issues/3154

On further inspection, the actual problem is that we have a Timedelta 
(full Python class, has a dict) allocated in a memory space sized for 
its parent _Timedelta (cdef class, no dict).

I don't know how this happened: the _Timedelta C struct is only created 
via its tp_new, which is passed the subclass (the standard Python 
mechanism for allowing subclasses to be larger in memory than their 
parent class - 
https://docs.python.org/3/c-api/typeobj.html#c.PyTypeObject.tp_new).