VM1 to VM2: The created_on date not migrated across for some tables

[mbarry]

The created_on date of order_histories, userinfos, vmusers should be based on the original date entry was created not the date of migration.

Scenario:
      Run the VM2 Migration tool with "everything" selected".
   
Issue:
      Inspection of the various virtuemart tables, note that the created_on date is the date of the migration run.

Solution:
      portUser()
        after line 615 insert
          $user['created_on'] = $this->_changeToStamp($user['cdate']);
          $user['modified_on'] = $this->_changeToStamp($user['mdate']);
           
        after line 695 insert
          $oldUsersAddi['created_on'] = $this->_changeToStamp($oldUsersAddi['cdate']);
          $oldUsersAddi['modified_on'] = $this->_changeToStamp($oldUsersAddi['mdate']);
           
      portOrders()
        after line 1476 insert
          $item['created_on'] = $this->_changeToStamp($item['date_added']);
 
        Note: I also show assignment to 'modified_on' however, this is always overridded by calls to setLoggableFieldsForStore() in vmtable.php

Affected files:
      administrator/components/com_virtuemart/helpers/migrator.php