Most current documentation on the Internet states that the correct way to disable the GNOME Shell screensaver is to simply set idle-activation-enabled to false:
$ gsettings set org.gnome.desktop.screensaver idle-activation-enabled false
With Fedora 19, changing idle-activation-enabled to false does not stop the screen from dimming and locking your screen.
In Fedora 19, this key is marked deprecated and ignored. You have to set org.gnome.session.idle-delay to 0 if you do not want to activate the GNOME Shell screensaver.
$ gsettings set org.gnome.desktop.session idle-delay 0