gnome-settings-daemon: Freeze break request for the mouse plugin

[Kalev Lember <kalevlember gmail com>]

Hi,

Bastien asked me to request a freeze break for
https://bugzilla.gnome.org/show_bug.cgi?id=708546

It's a simple patch that fixes a critical warning in touchpad settings
code, and also makes the setting actually work -- currently it always
fails to read back the value of the settings key.

Thanks,
Kalev