sendError(Exception…) should set the exception attribute on the response, since error.jelly handles this nicely.

core/src/main/java/hudson/model/AbstractModelObject.java

@@ -47,6 +47,7 @@ public abstract class AbstractModelObject implements SearchableModelObject {
      * Displays the error in a page.
      */
     protected final void sendError(Exception e, StaplerRequest req, StaplerResponse rsp) throws ServletException, IOException {
+        req.setAttribute("exception", e);
         sendError(e.getMessage(),req,rsp);
     }