Hi Zeo,
Be happy to help.
The name of the zip archive is 'autosave_a_3_0.zip' and it contains two items:
1) file 'autosave_a.py'
2) folder 'autosave_a'.
First install for your GIMP-2.8 to test it (should work OK) and second try it for your GIMP-Painter (not sure).
- stop GIMP if running
- move the old plug-in to a new location
- unzip the 'autosave_a_3_0.zip' archive in "...\.gimp-2.x\plug-ins" (user's plug-ins location)
- start GIMP and see if there is two new entries in the menu-image-bar under "<Image>/Extensions/Plugins-Python/File"
>"Auto save..."
>"NoUI auto save"
if yes the installation is finished
, if no: problems
...
Hope this answer about files.