[Mindwrapper] sorting listnodes

[Donnal W. <don...@ya...>]

I probably won't check in the revised branch module today, because
I want to change the observable mechanism for listnode first, but
today I added two new methods to listnode: 

    def Sorted(self, apath=''):
        temp = [(_getapathval(o, apath), o) for o in self]
        temp.sort()
        return [t[1] for t in temp]

    def Sort(self, apath=''):
        self[:] = self.Sorted(apath)

The Sorted() method returns a list that is sorted on any arbitrary
attribute path in each item, while Sort() sorts the listnode in
place using the same criteria. Usage would be like this:

    x.Sort('id.name.last')
or
    y = x.Sorted('id.name.last')


The _getapathval() function returns the value of the node specified
by the attribute path (apath) string. It is defined as:

def _getapathval(obj, apath):
    if apath:
        for attr in apath.split('.'):
            obj = getattr(obj, attr)
    return obj.Get()

The sort methods use the "decorate-sort-undecorate" (DSU) idiom
found in PythonIAN pp 400-401. This provides an efficient way of
sorting on any arbitrary components of the list items.

Regards,

=====
Donnal Walter
Arkansas Children's Hospital