fix ticket #631: temp leak when deleting slices

Cython/Compiler/ExprNodes.py

@@ -2605,6 +2605,7 @@ class SliceIndexNode(ExprNode):
                 self.start_code(),
                 self.stop_code()))
         self.generate_subexpr_disposal_code(code)
+        self.free_subexpr_temps(code)
 
     def generate_slice_guard_code(self, code, target_size):
         if not self.base.type.is_array:

tests/run/delete.pyx

@@ -60,3 +60,23 @@ def del_list_int(L, int i):
     """
     del L[i]
     return L
+
+def del_temp_slice(a):
+    """
+    >>> class A(object):
+    ...     attr = [1,2,3]
+    >>> a = A()
+    >>> a.attr
+    [1, 2, 3]
+    >>> del_temp_slice(a)
+    []
+    >>> a.attr
+    []
+    >>> del_temp_slice(a)
+    []
+    >>> a.attr
+    []
+    """
+    while a.attr:
+        del a.attr[:]
+    return a.attr