Wow, that works! Using WinXP (with WMP11 installed), I:
1) Installed Calibre v0.8.69.
2) Edited the plug in tweak as instructed, forgetting to hit apply.
3) Tried again and did it properly this time.
4) Calibre told me to restart Calibre, and I always do what I am told.
5) Calibre recognised my Nexus 7 running Android 4.1.1. It wouldn't before this.
6) I instructed Calibre to show books in the main memory of the device, and it listed absolutely everything on the Nexus 7.
7) I went back to the Calibre library on my PC, and instructed Calibre to send a book to the device that wasn't already on there, and it did as it was told. Good Calibre!
Well, it is working in WinXP for me! Thank you for your amazing work! Do you want me to test any other function of this latest version, Kovid?