I edited /etc/sudoers without visudo, and made a mistake. That will prevent you from successfully using sudo again. No real harm done, but it takes rebooting to get it fixed.
1) reboot in recovery mode (press escape when booting so the grub options are shown)
2) drop to a root shell (option in the recovery menu)
3) mount -o rw,remount /
4) visudo (emacs based editor)
5) reboot the system
You should be up and running again!
After more than a month of waiting for Android 4.2.2 I decided to go for it, and try the alternate route. I downloaded a Generic ES (Spanish) 4.2.2 ROM (read here), and flashed it to my phone. The downloading of the image and installing the flashtool are the timeconsuming tasks, flashing the ROM is a piece of cake. Be sure to not wipe the data and cache partition (untick 2 of the 3 checkboxes) if you want to retain what’s on your phone.
With the new Android I would be easy to acquire root, so DoomLord said. No unlocked bootloader or whatsoever needed. So I downloaded his tool, did what the screen said, and less than five minutes later I had a rooted-phone. Things couldn’t be easier than this.