Description of problem:
API call system.listLatestUpgradablePackages suggests not newest only packages. Both `yum list updates` and WebUI -> system -> Software -> Packages -> Upgrade shows only newest one.


Version-Release number of selected component (if applicable):
SWnightly as of yesterday
spacewalk-java-1.8.107-1.el5


How reproducible:
always


Steps to Reproduce:
1. wget 3 versions of some package, I had:
   drupal7-7.12-1.el5.noarch.rpm  drupal7-7.14-1.el5.noarch.rpm
   drupal7-7.14-2.el5.noarch.rpm
2. push them to some channel your system is subscribed to
3. Install oldest one (7.12-1.el5 in my case)
4. Confirm that `yum list updates | grep drupal7` and WebUI -> system -> Software -> Packages -> Upgrade only recommends newest (7.14-2.el5)
5. Check API call recommends two:
# python
Python 2.4.3 (#1, Dec 22 2011, 12:12:24) 
[GCC 4.1.2 20080704 (Red Hat 4.1.2-50)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import xmlrpclib, pprint
>>> client = xmlrpclib.Server('https://<fqdn>/rpc/api', verbose=0)
>>> key = client.auth.login('<user>', '<password>')
>>> pprint.pprint(client.system.listLatestUpgradablePackages(key, 1000010366))


Actual results:
[{'arch': 'noarch',
  'from_epoch': ' ',
  'from_release': '1.el5',
  'from_version': '7.12',
  'name': 'drupal7',
  'to_epoch': ' ',
  'to_package_id': 7761,
  'to_release': '2.el5',
  'to_version': '7.14'},
 {'arch': 'noarch',
  'from_epoch': ' ',
  'from_release': '1.el5',
  'from_version': '7.12',
  'name': 'drupal7',
  'to_epoch': ' ',
  'to_package_id': 7760,
  'to_release': '1.el5',
  'to_version': '7.14'}]


Expected results:
[{'arch': 'noarch',
  'from_epoch': ' ',
  'from_release': '1.el5',
  'from_version': '7.12',
  'name': 'drupal7',
  'to_epoch': ' ',
  'to_package_id': 7761,
  'to_release': '2.el5',
  'to_version': '7.14'}]


Additional info:
If this is expected, would it be possible to enhance documentation for the function so it warns about that?