i3lock improves slock by making it fork() and therefore combinable with
commands to suspend your computer. Additionally, instead of turning off your
screen via DPMS and/or displaying a black screen, i3lock displays a white
screen so you can see if your computer failed to resume from suspend or if
your screen is just locked. Also, when entering a wrong password, i3lock does
not call XBell(). This is important because i3lock/slock think you've entered
a password when resuming from suspend, at least sometimes.