xfconf optimisation

[Brian J. Tarricone]

Hey all,

I made a change to xfconf trunk so that when an xfconf/gobject property 
binding is created, it fetches the initial value of the property 
asynchronously.  While this doesn't reduce round-trips to the daemon (I 
have some other ideas for that which I'll work on later), it does allow 
apps to continue with their startup tasks while the properties are being 
fetched.

Now, there may be some unintended consequences, like apps initialising 
settings using default values, and then suddenly switching to the 
correct values after a (very) short time.

So... please test, especially on both really slow and really fast 
hardware.  If anything looks weird, I'll revert.  If it looks ok, I'll 
commit it to the 4.6 branch (it's only on trunk now).

	-brian