Bug#1131338: libfoundry-1-1: symlinks to devhelp manuals result in duplicates

[Simon McVittie]

Package: libfoundry-1-1
Version: 1.1~rc-1
Severity: normal
Control: affects -1 + manuals
Forwarded: https://gitlab.gnome.org/GNOME/foundry/-/issues/29

To reproduce: install manuals and libadwaita-1-doc. Run Manuals. Look in 
the "Debian GNU/Linux" folder in the sidebar.

Expected result: one instance of Adw-1 in the sidebar

Actual result: multiple duplicates

This is because we install symlinks to the libadwaita documentation in 
various places, to make sure that tools (and users) can find it where 
they would expect to look; and libfoundry does not de-duplicate them. 
I've opened an issue upstream, see link above.

Upstream previously tried to deduplicate, but the deduplication was done 
at the wrong level of the hierarchy and so was ineffective. I've opened 
https://gitlab.gnome.org/GNOME/foundry/-/merge_requests/27 with another 
attempt, but it needs some help with cache invalidation.

    smcv