Make polkit-kde-agent accept a wId for setting an explicit parent to the dialog

Review Request #100106 - Created Oct. 30, 2010 and submitted

Dario Freddi
jreznik, rnovacek
This patch adds a new DBus interface and a new method to Polkit Agent, which lets a client app (transparent through KAuth, patch incoming) set an explicit parent to the dialog. This is just an improvement and not a full solution, as the dialog cannot be made modal. The real solution would be providing in-process auth agents as we already talked about. Still, this already improves vastly the situation.
Works with the corresponding KDELibs patch.
Jaroslav Řezník
Reviewed before revieboard has been set up for polkit-kde-agent on IRC, all issues fixed. We agreed that action/wid matching should be enough (as a temporary solution).