HOTFIX: 2013.4, 2013.5 - New admin background progress window

The new admin background progress window will use an adaptive polling mechanism that will slow down and eventually stop polling when there is no activity.

Refreshing the page or opening the progress window will reset the counter and polling interval to normal values.

Polling interval:

* Default ("slow") interval - 7 seconds

* After 50 successive polls at the "slow" interval - 10 seconds

* After 75 successive polls at the "slow" interval - 20 seconds

* After 100 successive polls at the "slow" interval - paused

The "fast" interval for when the window is open is unchanged (every one second).