Fix/optimize Base.getModificationDate() and make it return ZODB date as fallback

Previous implementation only considered workflows that are chained to the
portal type:
- this is slower
- modification_date of old documents may change or disappear, preventing their
  reindexation
- edit_workflow was always considered, regardless it is chained or not

This commit makes getModificationDate more consistent: it simply iterates over
all workflow histories stored on the object.

When there is no workflow history, ZODB date is returned, which makes
getModificationDate useful for objects without any workflow chained, like
simulation movements.

Another optimization is that last history entry is accessed without loading
the whole history.

product/ERP5Type/Base.py

@@ -40,9 +40,11 @@ from AccessControl.PermissionRole import rolesForPermissionOn
 from AccessControl.SecurityManagement import getSecurityManager
 from AccessControl.ZopeGuards import guarded_getattr
 from Acquisition import aq_base, aq_inner, aq_acquire, aq_chain
+from DateTime import DateTime
 import OFS.History
 from OFS.SimpleItem import SimpleItem
 from OFS.PropertyManager import PropertyManager
+from persistent.TimeStamp import TimeStamp
 from zExceptions import NotFound, Unauthorized
 
 from ZopePatch import ERP5PropertyManager
@@ -3158,25 +3160,27 @@ class Base( CopyContainer,
 
       NOTE: this method is not generic enough. Suggestion: define a modification_date
       variable on the workflow which is an alias to time.
+
+      XXX: Should we return the ZODB date if it's after the last history entry ?
     """
-    # Check if edit_workflow defined
-    portal_workflow = getToolByName(self.getPortalObject(), 'portal_workflow')
-    wf = portal_workflow.getWorkflowById('edit_workflow')
-    wf_list = list(portal_workflow.getWorkflowsFor(self))
-    if wf is not None:
-      wf_list = [wf] + wf_list
-    max_date = None
-    for wf in wf_list:
-      try:
-        history = wf.getInfoFor(self, 'history', None)
-      except KeyError:
-        history = None
-      if history is not None and len(history):
-        date = history[-1].get('time', None)
-        # Then get the last line of edit_workflow
+    try:
+      history_list = aq_base(self).workflow_history
+    except AttributeError:
+      pass
+    else:
+      max_date = None
+      for history in history_list.itervalues():
+        try:
+          date = history[-1]['time']
+        except (IndexError, KeyError):
+          continue
         if date > max_date:
           max_date = date
-    return max_date
+      if max_date:
+        # Return a copy of history time, to prevent modification
+        return DateTime(max_date)
+    if self._p_serial:
+      return DateTime(TimeStamp(self._p_serial).timeTime())
 
   # Layout management
   security.declareProtected(Permissions.AccessContentsInformation, 'getApplicableLayout')