Fixed blurred content issue with iOS 5.

'translateZ(0)' causes the blurred content issue with iOS 5.

This code detects iOS 5 and disables 'translateZ(0)'.

related posts:

https://groups.google.com/forum/?fromgroups=#!searchin/iscroll/blur/iscroll/gU-UHFcxi8o/d0arMj5SqNEJ
https://groups.google.com/forum/?fromgroups=#!searchin/iscroll/retina/iscroll/DuZ5I-77fxo/wqZ9klysYgAJ