It is now a requirement for attachments to do one of three things:
  1. Have a content_type validation (e.g. "image/*")
  2. Have a filename validation (e.g. *.png, *.gif)
  3. Explicitly *not* have one of those validations

The intent is to make the default more secure, and you have to
explicitly reject the security of a validation in order to not have one.

AbstractAdapter wasn't delegating `binmode` or `binmode?` to the
underlying @tempfile object. `binmode` is useful for cases where the
Adapter object gets handed on to another library expecting an `IO`
object holding image data. We ran into this with Prawn and people using
`prawnto` in conjunction with Paperclip. Prawn wants to ensure the `IO`
is in binmode for embedding the image data.

Base64 encoded data-uris can contain newlines, make sure we handle
them correctly.

The ":" is a special character in file paths passed to ImageMagick's
"identify" command. Even though Cocaine (and everything else in
paperclip) escapes special characters correctly, we need to strip it out
of filenames to ensure identify (and probably other ImageMagick
commands) can run correctly.

* Based on rfc2822's commit ed05dc6b85f52ad88a83bc18e1986f3b75176740.

Rack gets a newline at the end of the content_type in certain instances: 'image/jpeg\r' which causes S3 to be unable to accept the file. Fixes #817

This PR allows you to assign a URI object to an attachment. The
attachment is downloaded and saved with a proper content type and
filename based on the path of the URL.

Fixes #902

This relates to #817

would cause the best_content_type to throw an error on trying nil.content_type.