RBVolumeButtons class no longer leaks
Added synthesize for justEnteredForeground so Xcode 4.3 can still build
Volume Buttons no longer start stealing when inited
Exposed start/stop methods for stealing volume
Demo app now has buttons to start and stop stealing volume
Added a retain to fix a warning
Deallocating the up and down blocks to prevent leaks
Added missing check to prevent stealing if it's already happening
Added asserts to prevent starting and stopping from being called from background threads
Removed redundant AudioSessionInitialize call
Setting the audio session to inactive when button stealing is off
Would always reenable stealing on app resume, even if wasn't stealing when backgrounded.
Now it only reenables if it was disabled on backgrounding
Removed protection around double-enabling during foregrounding.

There's already general protection around double-enabling.
Avoid flashing the volume indicator when starting from a 0% or 100% volume level
Fix notifications' handling

- removeObserver:self doesn't work with addObserver:…usingBlock:!
- UIApplicationDidEnterBackground/ForegroundNotification are redundant when using UIApplicationDidBecomeActive/ResignActiveNotification
Merge branch 'refs/heads/fix_notifications_handling'
Fix demo project warnings
Merge pull request #6 from rivera-ernesto/v2

V2