Forum attachments reform. - Add new style of attachments to the forums, allowing multiple attachments to a single message directly from the message post page, using the multiple file input widget. - Retain compatibility with old style attachments, using the new 'AttachmentStyle' package instance parameter. Currently, this supports two values: 'simple' (new behavior) and 'complex' previous behavior. - Both attachment styles can coexist, and attachments added by any of such methods will be shown. - Improve the contract on 'forums/lib/message/post.tcl'. - Show attachments on message preview. - Bump version number.