Re-filter the pending notification when we notice that there is noone

listening to one of them. This can happen if the corresponding signal
has been disconnected in the meantime, which e.g. the recent
optimizations in AgentBase do.
Also, change the filtering from O(n²) to O(n) while I was at it.

svn path=/trunk/KDE/kdepimlibs/; revision=1209556