[libcontacts] kick off an UpdateRequest when contacts start to come in

This patch increases the speed of loading contacts by 30% on my device (that is with 10k contacts in the db).

Without it, the seasidecache in the FilterAll phase first adds all of the contacts to m_contactsToAppend before starting to process them in applyPendingContactUpdates.
m_contactsToAppend is a complex structure :) it lists contacts per FilterType, and the code before this establishes that there's no list for this type. (Elsewhere there is code for removing the entry for this type when its list goes empty)

I don't think I really understood your question though, so feel free to explain if I didn't answer it here.