Add SIGWINCH. This is extra important now that I have virtualbox guest additions with automatic resize. Implement this in the editor, pager, shell, and other places. Do something similar for graphical programs, the games and trianglix sort of work due to re-rendering all the time, but programs like login(8) should be notified of a new resolution so they can re-render (or better yet, don't make such changes while they run, but give them the new resolution request, and let them do the mode setting at convenient times). Marking as release-blocking because this can be a bad usability failure.