[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.
@amtep: Sorry, missed part of your question - if the m_contactsToAppend structure already has list(s) of another filter type, then the kick isn't required?  That's how I parse your comment here. If we need the kick in any case, then keep the code and change the comment :)