As discussed on python-dev, silence three gcc-4.0.x warnings, using assert()

to protect against actual uninitialized usage.

Objects/longobject.c: In function ‘PyLong_AsDouble’:
Objects/longobject.c:655: warning: ‘e’ may be used uninitialized in this function

Objects/longobject.c: In function ‘long_true_divide’:
Objects/longobject.c:2263: warning: ‘aexp’ may be used uninitialized in this function
Objects/longobject.c:2263: warning: ‘bexp’ may be used uninitialized in this function