1.21:
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 * Better check non category addData

1.20:
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 * Add category depth to the category-tree option
 * Improve constants

1.19:
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 * Fix to allow fetching categories by author by adding global $serendipity array
 * Add PLUGIN_EVENT_ENTRYCHECK_LOCKING description
 * Add ChangeLog

1.18:
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 * Remove WYSIWYG warning

1.17:
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 * Use lang API - extends required version
 * Fix error (preview) messaging

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