Merge pull request #4 from theojulienne/master

Add OS X support to podspec
fix travis-ci URL
Declare connected in the correct location
add  WITH_THREADING for libmosquitto threading support
fix connected property

set connected property in on_connect callback based on the return code
value.

fixes #8
Update Xcode project settings
add cleanSession support
remove deployment target
bump ios.platform to 6.0

required to use dispatch_queue_t as regular Objective-C (for ARC
support)
add deployment target 6.0
add back mosquitto's WITH_THREADING preprocessor macro

removed by mistake in 0c0c013
Fix potential memory issue for applications with high throughput.