OK, the good news is: I now see the master slide's text being
extracted; thanks Nick!
But the bad news is: we are now also extracting all the "boilerplate"
text that is included in the master slide by default.
For example if I open Powerpoint 2007, make no changes and just save
that one blank slide as PPTX, then get the text from it using TikaCLI, I see
Click to edit Master title style
Click to edit Master text styles
This is the boiler-plate text from that initial title slide's master
slide. I think we should somehow not include it, but, I have no idea
how... does PPT/X somehow note that this is "fake" boilerplate text!?
Somehow Powerpoint knows not to display this when I view the slide...