"you have new update" icon may launch multiple instances of update-manager

[K.C. Leung]

Although Update Manager does not allow multiple instances of itself if it is run via the System menu, a user may still end up running 2 instances of Update Manager if he does the following steps:

1. The user clicks on Update Manager in the System -> Administration menu.
2. He reloads the packages list, and Update Manager informs him there are new updates. The "you have new updates" icon will pop up in the system notification area. This may happen before the package list is finished reloading.
3. If he now clicks on the "you have new updates" icon, a new instance of Update Manager will be launch to show the update(s), even as the first instance continues to run and the packages list continues to download.

This is a problem because the new instance of Update Manager may not show all the updates, as the packages list may not have finished reloading yet.

[Sebastian Heinlein (glatzor)]

Perhaps we should extend the lock to the download period, too.

Sebastian