Changes

** 404 redirection*** do not redirect obvious custom server error pages*** when we do redirect, original error page is available at one click.*** use some heuristic beyond simple page size for identifying default 404 pages**** compare to standard Apache and IIS 404 pages, possibly fuzzy (use edit distance?)**** use EndDocumentLoad (or other event) + redirect**** can't do deep docshell changes for 3.1***** should unify with existing error page architecture in v.next.**** similar to how the Friendly Error extension works now**** implement listener in C++, should be able to access 404 status directly from document.*** use 404 specific error page for 3.1 rather than trying to re-use the generic network error page.**** more design flexibility**** easier to get in before string freeze**** unify with generic network error page in v.next

** DnsNotFound:*** Extend existing error page with alternatives drawn from Places.*** Add one-click access to Google Link Doctor.*** Other tools.*** Improved design**** May be constrained by the generic network error page architecture.

** Constraints*** String Freeze for Beta 4: Mar 19, 2009*** Code Freeze for Beta 4: April 6, 2009