add migration to increase string limit, and updated redirects in transfrom controller

Hey Ben. Thought I would give a pull request a shot. In the transform_controller any instance of:

    redirect_to :action => ... :image_set_id => config[:image_set_id]

...I changed to...

    redirect_to :action => ... :image_set_id => @image_set.id

On the migration addition I was getting some errors in mysql because the action was longer than 20 chars, so I increased that to 100.

After these changes I'm getting this error http://pastie.org/9584439 on transform/date_format_form?image_set_id=3 (