PPTX text from diagrams not extracted

Created by: Anonymous

Original issue 329 created by @ysavourel on 2013-04-24T15:27:19.000Z:

It looks like text from diagrams files are not extracted from PPTX document.

For example in ppt/diagrams/dataNN.xml the elements <a:t> content where xmlns:a="http://schemas.openxmlformats.org/drawingml/2006/main"