Update jquery.frontend.js

This fixes the jquery frontend javascript file in Internet Explorer 7
Merge pull request #497 from WouterSioen/patch-10

Update jquery.frontend.js. Make it IE7 compatible.
Drop IE7 emulate in backend

Not resetting the CKEditor in the pages module makes it possible
to stop emulating IE7.
Bugfix: copying pages wasn't working due to the csrf-check.

To resolve this we extend from BackendBaseActionIndex instead of
BackendBaseActionDelete where the csrf-check is performed automatically
Groups: bugfix: double usage of variable caused unexpected behavior.
Merge branch 'master' into 3.6-wip