Fixed an issue with destroy.
Fixed an issue with destroy.

dashifen/jquery-backstretch,jokase/jquery-backstretch,danielgindi/jquery-backstretch,danielgindi/jquery-backstretch,jquery-backstretch/jquery-backstretch,jokase/jquery-backstretch,dashifen/jquery-backstretch,jquery-backstretch/jquery-backstretch,srobbin/jquery-backstretch