Xiaoming Lu's changes:
Background
========
Need a way to upload image using file_column, save image to tmp, upload the 
image to Amazon s3 in before_save, and then save the Amazon cloud url (starting with
http://) to database.

FEATURES 
========

Let's assume an model class named Entry, where we want to define the "image" column
as a "file_upload" column.

class Entry < ActiveRecord::Base
  file_column :image
  before_save :update_image_url

  def update_image_url
    if ((self.image_url != nil) and File.exists?(self.image_url))
      ss = MetaChannels::Thumbnails::StorageStrategy::AmazonS3StorageStrategy.new
      new_image_url = ss.store_featured_item(self)     #store tmp image to s3, update image_url with s3 url
      new_image_url = new_image_url.to_s().strip()
      self.image_url = new_image_url
    else
      # after user upload a file, the file path needs to be valid so that file can be uploaded to s3
      logger.error("ERROR: image file does not exists")
    end
  end

end

* every entry can have one uploaded file, the filename will be stored in the "image" column

* files will be stored in "tmp", then file will be opened from tmp and upload to Amazon s3,
  tmp file will be deleted

* When Entry is saved, Amazon Cloud url of the file (starting with "http://" will be saved 
  into the database. 

* in a view, "<%= file_column_field 'entry', 'image' %> will create a file upload field as well
  as a hidden field to recover files uploaded before in a case of a form redisplay

* in a view, add Entry/_image_url_form_column.html.erb to display image. 
<label><%=column.name.to_s.titleize %>:</label>
<dl>
  <dt> <label><%=column.label%>:</label> </dt>
  <dd>
    <% if (@record.image_url and @record.image_url.include?("http")) %>
       <%=link_to(image_tag(@record.image_url, {:width=>"50", :height=>"50"}), @record.image_url, :popup => true)%>
    <% elsif @record.image_url %>
      "NO IMAGE (<%=@record.image_url%>)"
    <% else %>
       "NO IMAGE"
    <% end %>
    <br/> Image Upload: <%= file_column_field 'record', 'image_url' %>
  </dd>

</dl>

Note that url_for_file_column is deprecated in this file_column and please do not use it. 

USAGE
=====

Just drop the whole directory into your application's "vendor/plugins" directory. Starting
with version 1.0rc of rails, it will be automatically picked for you by rails plugin
mechanism.


BUGS & FEEDBACK
===============

Bug reports (as well as patches) and feedback are very welcome. Please send it to
xiaoming.lu.backup@gmail.com