[Tracker] async-queues-due branch merged

[Martyn Russell <martyn lanedo com>]

Hi all,

I just merged the work Jürg and Carlos did last week to use 2 
GThreadPools for handling updates and queries to the Tracker database. 
This achieves a few niceties:

 - Readonly queries in parallel (currently 2, tested with more)
 - Timeouts and query cancellation for abusive queries (>15s right now)
 - Now tracker-store is more responsive generally (times out much less)

This merge to master now means that we depend on SQLite 3.6.17. As I 
just discovered, this means that you will have to get packages to 
upgrade on Ubuntu (perhaps other distros too). So if you git pull, this 
is a heads up.

--
Regards,
Martyn