make an old test from 'broken' directory usable

--HG--
rename : tests/broken/voidstarcast.pyx => tests/run/voidstarcast.pyx

tests/broken/voidstarcast.pyx → tests/run/voidstarcast.pyx

 cdef class C:
     cdef int i
 
-cdef int f() except -1:
+    def foo(self):
+        self.i = 42
+
+    def get_i(self):
+        return self.i
+
+
+def cast_cast_cast(arg):
+    """
+    >>> x = C()
+    >>> x.foo()
+    >>> cast_cast_cast(x) == x
+    True
+    >>> x.get_i()
+    42
+    """
     cdef object x
-    cdef void *p
+    cdef void *p = <void *>arg
     cdef int i
     x = <object>p
     p = <void *>x
     x = (<object>p).foo
     i = (<C>p).i
     (<C>p).i = i
+    return <object>p