Give -[IssueManager refresh] a callback instead of a return value.
Switch IssueManager to use callback blocks in its refresh method.
Take network calls off the main thread.
Use of dispatch_get_current_queue() is recommended only for debugging. Use main queue instead.
Fix merge errors.
Merge branch 'master' of https://github.com/Simbul/baker into async-networking
Merge remote-tracking branch 'origin/master' into async-networking

Conflicts:
	BakerShelf/ShelfViewController.m
Add NKDontThrottleNewsstandContentNotifications constant so can receive more than one Newsstand download notification per day while in debug mode
Add semaphore so that magazines can be downloaded in the background
Move the semaphore so that it only gets used when app is in the background
Merge sdarlington async networking pull request
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 branch 'master' into sdarlington-async-networking