Add exception message to avoid exposing class

[j15e]

This exception class is added to the model errors and shown to the end-user as is (Errors::NotIdentifiedByImageMagickError), because there is no message attached to it.

The exception is added as a processing error here:

kt-paperclip/lib/paperclip/attachment.rb

Lines 537 to 540 in 11abf22

	rescue Paperclip::Errors::NotIdentifiedByImageMagickError => e
	log("An error was received while processing: #{e.inspect}")
	(@errors[:processing] ||= []) << e.message if @options[:whiny]
	ensure

And the the processing errors are transferred to the model here:

kt-paperclip/lib/paperclip/attachment.rb

Lines 574 to 578 in 91923a6

	def flush_errors #:nodoc:
	@errors.each do |_error, message|
	[message].flatten.each { |m| instance.errors.add(name, m) }
	end
	end