Description of problem:
alacarte doesn't modify sub items in system menu.

Version-Release number of selected component (if applicable):
alacarte-0.10.0-1.fc6.noarch


How reproducible:
always

Steps to Reproduce:
1. click system menu on alacarte
2. check or uncheck item
3.
  
Actual results:
nothing

Expected results:
allow changes

Additional info:

starting alacarte from the command line and try to change a item on the sytem menu yields:
Traceback (most recent call last):
  File "/usr/lib/python2.4/site-packages/Alacarte/MainWindow.py", line 372, in on_item_tree_show_toggled
    self.editor.setVisible(item, False)
  File "/usr/lib/python2.4/site-packages/Alacarte/MenuEditor.py", line 208, in setVisible
    menu_xml = self.__getXmlMenu(self.__getPath(item), dom, dom)
  File "/usr/lib/python2.4/site-packages/Alacarte/MenuEditor.py", line 475, in __getXmlMenu
    node = self.__addXmlMenuElement(element, name, dom)
  File "/usr/lib/python2.4/site-packages/Alacarte/MenuEditor.py", line 486, in __addXmlMenuElement
    return element.appendChild(node)
  File "/usr/lib64/python2.4/site-packages/_xmlplus/dom/minidom.py", line 1548, in appendChild
    raise xml.dom.HierarchyRequestErr(
xml.dom.HierarchyRequestErr: two document elements disallowed