AttachmentRenderSupport does lots of unnecessary work

In September 2007 the attachment-rss-content.vm was rewritten such that Attachment items in RSS feeds contain only minimal information: What attachment was modified, who modified it, when, what page/blog it's on. The class that invokes that template and provides the Velocity context was left unchanged. It gets the full history of the attachment and renders the page/blog the attachment is on into html, which can take considerable time if it has macros on it.

This can cause major issues from a performance point of view when somebody attaches multiple things to a page with an attachments macro on it, particularly considering CONF-21373.