reloads by students who prop their books on the F5 key.
backport (dpvc): Corrected comment indicating time was in micro- rather
backport (dpvc): Completely rewrote the file to use a different
technique. Instead of looking for unbeforeunload events (which didn't
work reliably, since Firefox will reload the page before it has a chance
to install the handler), we look for F5 key events and F5 ignore keydown
events, but reload the page on F5 keyup instead. This skips the
autorepeating keys and only reloads the page when the user lets go of
the key. So there is only one reload. After several autorepeated F5
keypresses, a dialog will appear asking you to check if something is
holding down the F5 key.
backport (dpvc): Added comments about how to install the file.