Make BigIntegerKiller's warning message more precise.

Interesting boxtree failure. Could it be related to https://github.com/inducer/boxtree/issues/4?

https://gitlab.tiker.net/inducer/sumpy/builds/19854

That's my current theory. This reemerged after I re-upgraded the Nvidia drivers. With two of the more competent CLimplementations suggesting the issue might be on our end, I think it at least can't hurt to look. Pekka seemed to have a pretty good lead.

@inducer: Given that the failure in boxtree is irrelevant, can this go in?

Yeah, sorry. Totally snoozed on this.

mentioned in commit 1511d20e

merged