Before the error message was sometimes millions of characters long.

> [paperclip] Content Type Spoof: Filename a.csv
> (application/octet-stream from Headers,
> [#<MIME::Type::Columnar:0x007f9f90f89fa8
> @container=#<MIME::Types:0x007f9f90b09d98 ... snip millions of
> characters of output here ...>], @content_type="text/csv",
> @raw_media_type="text", @raw_sub_type="csv", @simplified="text/csv",
> @i18n_key="text.csv", @media_type="text", @sub_type="csv",
> @extensions=["csv"]>] from Extension), content type discovered from
> file command: application/zip. See documentation to allow this
> combination.

Now becomes:

> [paperclip] Content Type Spoof: Filename a.csv
> (application/octet-stream from Headers,
> ["text/comma-separated-values", "text/csv"] from Extension), content
> type discovered from file command: application/zip. See documentation
> to allow this combination.

[fixes #2017]