test case for 'cdef extern class' definitions in .pxd files

tests/compile/crunchytype.h

+
+struct CrunchyType {
+  int number;
+  PyObject* string;
+};

tests/compile/crunchytype.pxd

+cdef extern from "crunchytype.h":
+    cdef class crunchytype.Crunchy [ object CrunchyType ]:
+        cdef int number
+        cdef object string

tests/compile/extimportedsubtype.pyx

+from crunchytype cimport Crunchy
+
+cdef class Sub2(Crunchy):
+    cdef char character
+
+cdef class Sub1(Sub2):
+    cdef char character