Temporary server problems can cause errors in rendering of images and
math; the cached entries then sit around for hours/days/weeks, and
people whine about them long after the problem is solved.

It would be valuable if such errors could set a flag on the
ParserOutput object for an early cache expiration.

(Some limited time, rather than no caching at all, is probably wise
to limit load during the problem period.)

Version: 1.7.x
Severity: enhancement