file_column - on_save Proc and marsheling

Hi All,

Using file_column, when I set a file_column field to nil file_column
adds an on_save method using a Proc. This blows away marshalling and
hence the ability to store this model into a session once I have
nilified the field.

    def on_save(&blk)
      @on_save ||= []
      @on_save <<

Has anyone got a fix or workaround for this?
I am using file_column 0.3.1