Make the tasks in the dock correspond to the current workspace only

In order to use AWN as a replacement of the original gnome lower panel, only the tasks of the current workspace should appear in the bar.

That can already be easily done in gconf-editor by de-selecting the option "all-windows" (or something like that), but it would be nice if that was integrated in the configuration panel.

Also, when this option is selected, something quite annoying arises: when switching workspace, the tasks disappear, but the HORIZONTAL REPLACEMENT f theother icons is really really slow (especially when switching from a workspace with severl tasks to an empty workspace). This is related to this blueprint: https://blueprints.launchpad.net/awn/+spec/faster-icons-replacing

Maybe when switching workspace, the icons should instantly appear at the right place (without a moving animation).