Allows a lambda to be passed to decide what format a style should
be processed as

There are some file types that the file command doesn't understand.
Notably, files that have a format, but are ASCII-text based (like ruby,
certificates, etc), show up as text/plain. This presents a problem,
because the mime-types gem either doesn't report them at all (as for
.pem files) or reports them differently (as for .rb files).

This change allows a Paperclip.options[:content_type_mapping] hash,
which allows for a mapping of { :pem => "text/plain" } which tells the
spoof detector that this is an OK matchup and to allow it.

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.

Use hexdigest to ensure that tempfile names will be a reasonable length.  Remove illegal filename characters check since it is no longer relevant when doing a hexdigest on the filename

pry-debugger doesn't compile on JRuby, and we're really only using that
locally.

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

Content Type errors were incorrectly being set as an array on the base
attribute rather than being set individually as strings.

Copying attribute validation failures up to the root object breaks the
validate_attachment_presence_matcher when other paperclip validations
have failed.  This fixes this bug.