We get a lot of packaging bugs for third-party builds in our tracker,
especially since our debug tool now opens directly our bug tracker.
It would be preferred if third-party packagers were to make a first
filtering of bugs and only reported once they knew for sure that the bug
is in core code, and not in packaging.

Our configure script will now propose a --with-bug-report-url option
allowing to set a different web address. This address will be the one
opening in the debug dialog.