Add media-type spoof detection
Add stub to fix HasAttachedFile tests
Calculate data-uri file names off the validated content-type
Remove test invalidated by better content-type detection semantics
Fix s3 test for new file naming and content type detection semantics
Fix stringio name in tests
A missing content_type validator shows deprecation warning
We can't work with isolated attachment objects anymore
We can't work with isolated attachment objects anymore
StringIOs have different names by default now