Allowed Filename Characters, option limit to ISO-9660 characters

ISO-9660 (file system for CD-ROMs) limits filenames to uppercase letters, digits, dot, and underscore. No dash (-) or lowercase letters. This could be another restriction for uploaded filenames, if a sysop was planning to archive the files to ISO-9660 storage.

This would be a more restricted character set than the "Safest subset" and likely cause rejection of a lot of uploaded files, so then we might want to have uploaded filenames auto-converted (upper-cased, dashes converted to underscores). Maybe nobody really needs this. Just an idea, now that I realize how restrictive ISO-9660 really is.