Fix broken lightdm

After some system upgrade, lightdm broke on my computer (Ubuntu 12.10).

The symptom was the following: I can enter my password but when I hit <Enter>, I don’t log and I go back to lightdm screen.

As a workaround I logged with a tty (<Ctrl> + <Alt> + <F1>) and remplaced lightdm with gdm:

# Install gdm
sudo apt-get install gdm
# Set gdm as default display manager
sudo dpkg-reconfigure gdm

But the problem was just the read access to ~/.Xauthority, so the solution was simply to remove that file:

rm ~/.Xauthority