Products.externaleditor

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- Fixed reflective XSS in findResult.
This applies PloneHotfix20170117. [maurits]

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- Quote variable in manage_tabs to avoid XSS.
From Products.PloneHotfix20160830. [maurits]

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- Moved code to https://github.com/zopefoundation/Products.ExternalEditor

- Update dtml to Zope trunk.

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- Added support for unaware mimetype browser - we now add the .zem extension no
matter what the user-agent

- Modified the cache's parameters - special case for MSIE

- Corrected and added tests

- Moved the sources of the client to another package : collective.zopeedit

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- Update manage_main, manage_tabs, and findResult monkey patches to include
fixes from Zope 2.12.

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- Removed imports from Globals.

- Purged old Zope 2 Interface interfaces for Zope 2.12 compatibility.