pages: fixed cached data when `url_cache` is used: `request.template_data` and `request.data` where cached using a shallow copy, causing trouble when a mutable object was used. This has been fixed by using a deepcopy, which should not be a resource issue as `request.data` and `request.template_data` should contain a few data in most cases.

The work in this directory and subdirectories have been made by Andreas Gohr and the Dokuwiki community.
All the work is available under Creative Commons BY-SA.
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