The following patch introduces a new function for restricting search results to messages within a certain look-back time. For instance, if the time specification '3w' is given then the search will be restricted to messages received within the last three weeks. The second patch binds this function to the 'S' key. I have a feeling that Carl won't be into this patch, but I'm throwing it out there anyway, just in case. On my slow machine, use of this function speeds up searches considerably, especially since most of the time I'm just searching for recent messages anyway.