The "Updates" tab in "plugin manager" shows previously updated plugins. Perhaps the plugin
manager can get the version info from the plugin .hpi file?

Steps to reproduce:
1. Go to the update manager and "updates" tab
2. Update a plugin
3. Go to hudson main page
4. Go to the update manager and "updates" tab

Expected outcome:
The previously updated plugin is not displayed in the list

Actual outcome:
The previously updated plugin is displayed in the list as an available update