Add documentation for including `aws-sdk` in Gemfile

Add ':keep_old_files' option to `has_attached_file`

Set this option to `true` will make paperclip retain your file from the storage engine.

From https://github.com/pcreux/paperclip/commit/52374958ef83f1641cf008aead27c23b25fb842d

Conflicts:

	lib/paperclip/attachment.rb

This fixes #660

This is necessary so Gemnesium will be green.

Standardize strip with resy of application.  Without to_s, causes errors like "undefined method `strip' for image/bmp:MIME::Type".

In some case, we seriously don't want to prepend the timestamp with & if there wasn't a query string there. If the original URL doesn't have any query string, we should add the ?.

There was some problem with command line parsing with a special character.

The original commit came from @amazonwebservices and @trevorrowe in #579.
I had to revise the commit and make sure all the test cases are passing.
All credits still goes to those guys, thanks a lot!

    This can be used in migrations, i.e.

      create_table :users do |t|
        t.has_attached_file :avatar
      end

(three commits squashed into one by Alexey Mahotkin <squadette@gmail.com>)

Remove the Options class, replacing it with a hash.

This will fix the problem on the CI server, where some time the change occurred by "write_file" will not trigger Rubinius to generate a compiled .rbc file.