Add trip review functionality.

triplist.php - show all of the trips for a given user, or for me if no user specified.

trip.php - show all of the rides ridden on a given day.
Prevent some 'unset variable' warnings
Remove unnecessary ?> at end of various files

This is a good idea because it ensures these files won't echo anything
if they weren't meant to; if they did, this could cause problems with
headers and cookies in later files.