Initialize CBReplication.status to ‘offline’ in the -start call

This makes tracking the status easier. Before this change it would stay at ‘stopped’ for a little while
until the background replicator thread started up.
Fixed target OS requirements

* Some iOS targets were still set to iOS 5; updated everything to iOS 6.
* Updated Mac OS target to OS X 10.8.
* Added a (strong) annotation to a dispatch_queue_t property in CBLManager.h
to avoid a warning with OS X 10.8+.
* Updated ErrorUtils in MYUtilities to stop using a deprecated function.
Fixed crash in WebSocket-based _changes feed handling an HTTP redirect

Fixes #246
Minor tweak to unit test to suppress static-analyzer warning

Just marking a variable as unused.