Show an error message when S3TC support is missing
Via #2799 (closed)
When the user has no support for S3TC texture compression installed, we should show an appropriate error message. Currently we just get white textures, which isn't exactly useful in discerning the cause of the error.
We should only show this error when S3TC is actually used. Morrowind uses it, but a total conversion might not.
(RM-2800 from redmine: created on 2015-07-26 by scrawl ., , closed on 2015-07-29 by scrawl .)