Date Context breaks context edit form

Issue Summary

Hello,
I'm using jquery_update to run jquery 1.8 in our themes and I've noticed that the date context plugin throws a jquery error on the context edit form:

Uncaught Error: Syntax error, unrecognized expression: #:input[name="conditions[plugins][date_context_date_condition][options][operation]"]

After some quick research, I stumbled across the use of the jquery selector ':input' to be deprecated as of jquery 1.7.

Looking at the date_context plugin code, it occurred to me that the use of ':input' as a '#dependency' selector is not standard. All other instances I could find using the ctools form helper '#dependecy' use the element id as the primary argument rather than a more generic input selector.

The included patch switches to this more standard use of '#dependency' and resolves the future-proofing issue with jquery.