xdg-utils is finally there:
apt-cache madison xdg-utils
xdg-utils | 1.0~beta3-1 | http://archive.ubuntu.com edgy/universe Packages
** Changed in: lyx (Ubuntu)
Status: Fix Committed => Fix Released
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Please sync xdg-utils and lyx-common from Debian
https://launchpad.net/bugs/57478