patch against r59327
Currently, when uploading files, the contents of the upload form's "description" field are used as both the upload summary and the inital text of the description page. This makes things simpler and is probably best kept that way on the user-facing upload form.
However, the first ~200 characters of the description page do not always make a good summary, and it is a pain to have to upload with an appropriate summary and then separately edit the file description page to add a description. It would thus be useful, especially for bulk uploads, if API clients could specify a separate summary and page text. MediaWiki already supports this internally; the accompanying patch adds support to the API.