Thanks for this
I wonder why this couldn't be in core moodle ?

ah i realised we can use a little more info here (https://moodle.org/plugins/edit.php?plugin=local_eduweb_databasefiledownload):
consider adding to useful links:
- code repository
- documentation and any other useful links

I tried to install the plugin, but I got this error message:
Fatal error: Call to undefined function xmldb_local_databasefiledownload_install() in /lib/upgradelib.php on line 447
After this the plugin appears installed in Local Plugins, but there isn't anything in database administration menu.
Can anyone help me about this? Thank you.

Please note that in Moodle 2.4, the extra 'tab Download users files' do not appear.
In full debug mode Moodle displays :

Deprecated local plugin navigation callback: Please rename
'eduweb_databasefiledownload_extends_navigation' to
'local_eduweb_databasefiledownload_extends_navigation'. Support for the old
callback will be dropped after the release of 2.4

line 322 of /mod/data/view.php: call to core_renderer->header()

Cheers

Here is a version that seems to work also in Moodle 2.4 and add the ability to also retrieve picture fields

https://github.com/patrickpollet/moodle_local_eduweb_databasefiledownload

Cheers