Added correct work of "recognizesPanGesture" bool
Check _centerPanel exists

Check that _centerPanel exists before removing it's observers
Fix issue #46 - Pre iOS6 check

Implements fix supplied by @timprepscius
Merge pull request #62 from alias1/checkBeforeRemoveObservers

Check _centerPanel exists
Merge pull request #64 from alias1/fixPre6Check

Fix issue #46 - Pre iOS6 check
Merge pull request #44 from itruf/patch-1

Added correct work of "recognizesPanGesture" bool