Fix some crash issues of SoundFlowebed when sleep/resume, or sudden device disconnection.

Some people claim SoundFlowerbed crashes when sleep/resume, or device disconnection, so I am.

I've made some fixes, so now It merely crashes when sleep/resume, or sudden device disconnection.

My changes also includes:
1.Change development target to OSX10.7, because my latest XCode does not support 10.6 or earlier.
2.Stop using [NSThread detachNewThreadSelector]. Manipulating UI components from outside of main thread is danger.

Could someone test/review my patch?

I noticed even after my change adapted, some issues are remain.
1. Disconnection of Firewire devices during sleep can't be handled well.
2. Selecting "AirPlay" does not work well.
I'll tracking these issues.