Avoid running out of file descriptors when backing up many objects in the...

Avoid running out of file descriptors when backing up many objects in the trash upon bt5 installation.

Before, when installing a bt5 whose format has changed, many subobjects may
end up being backup up, but it keeps one FD per subobject, thus easily
reaching the limit of 1024 FDs (as given by ulimit -Sn/-Hn).

This is a followup of b71e5a73 specific to TrashTool as that commit seems to
only fix the issue when TrashTool is not used.

product/ERP5/Tool/TrashTool.py

@@ -37,6 +37,7 @@ from Products.ERP5 import _dtmldir
 from zLOG import LOG, WARNING
 from DateTime import DateTime
 from Acquisition import aq_base
+from cStringIO import StringIO
 
 class TrashTool(BaseTool):
   """
@@ -145,9 +146,10 @@ class TrashTool(BaseTool):
         obj = self.unrestrictedTraverse(object_path)
       if obj is not None:
         for subobject_id in list(obj.objectIds()):
-          subobject = obj.unrestrictedTraverse(subobject_id)
-          subobject_copy = subobject._p_jar.exportFile(subobject._p_oid)
-          subobjects_dict[subobject_id] = subobject_copy
+          subobject = obj[subobject_id]
+          subobjects_dict[subobject_id] = subobject._p_jar.exportFile(
+            subobject._p_oid, StringIO())
+
           if save: # remove subobjecs from backup object
             obj._delObject(subobject_id)
             if subobject_id in obj.objectIds():