daap: make password prompts work properly (bug #666338)

 _________________________________________
/ finish authentication in the mount      \
| operation's reply signal rather than    |
| doing stupid mainloop tricks. also free |
| password lists returned by              |
| gnome-keyring and clear the connection  |
| pointer when releasing it so            |
\ disconnecting actually finishes         /
 -----------------------------------------
        \   ^__^
         \  (oo)\_______
            (__)\       )\/\
                ||----w |
                ||     ||