Make real request and response objects available during Word export

Currently in the Word export, the request object is a stub that doesn't include the parameters which are passed to the Word servlet.

We can improve this by setting the ServletActionContext request and response objects appropriately. These will be picked up by macros and other code using VelocityUtils in the page rendering.

A patch for Confluence 3.0 and later is attached. To install it, put ExportWordPageServer.class and ExportWordPageServer$1.class into confluence/WEB-INF/classes/com/atlassian/confluence/servlet/, creating that directory if it doesn't already exist.