Make inactive-selection-is-different configurable. The default (for now) is off as Robert Knight complained strongly about performance problems (not that I've noticed any, but it seems I'm overridden). Alas for the usability...

Maybe if I am lucky enough people will complain about the change to make the default "on" ;-).

TODO: Qt 4.5 will hopefully improve its slowness enough that we can make it enabled by default without objection.