Merge sdarlington async networking pull request
Push status for refresh button is now visible

Fixes #947.
Wrapped code to handle the download of a issue in response to a newsstand notification in block passed to the refresh call as a success callback
Updated getShelf and getPurchases JSON methods to check for the thread they are called on and decide to execute the code in a background thread (returning to the main thread for the last callback) or in the one they are currently in. Whit this the background operations (like the newsstand handling) doesn't have to wait for the main thread to start running
Whoops! This was wrongly deleted during the last merge, fixed.
Merge branch 'master' of git://github.com/Simbul/baker into sdarlington-async-networking
Merge commit 'a21c0c8146b40b544a8c982194ff79dfb59ac9e9' into newsstand_notification

Conflicts:
	Baker/AppDelegate.m
	BakerShelf/ShelfViewController.m