Currently I modified:
admin/views/layout.html
admin/views/default/index.html
admin/views/default/site.html
admin/static/js/web2py.js (flash message box)
admin/models/buttons.py (only added bootstrap class selectors)
admin/controllers/default.py (only added bootstrap class selectors)
and added
admin/static/css/bootstrap_essentials.css
admin/static/css/bootstrap_adapters.css
admin/static/jmages/menu_responsive.png
+ ,of course, bootstrap files
I hope that this changes should be acceptable.
I splitted the css code in 2 files (bootstrap_essentials, bootstrap_adapters) because my goals are:
to maintain backward compatibility (admin interface will work alse with original file styles.css alone)
to build a simple bootstrap look and feel layout (by adding bootstrap files and bootstrap_essentials.css) working without other css files and so compatible with bootswatch customizations
to port admin interface on top of bootstrap preserving the artwork (by adding bootstrap_adapters.css)
I think to provide a more complete draft of the code in the few next weeks.