I had made a mistake and the notes on the wiki do work for me (I found I didn't need the entry in /etc/modules though). Anyway an updated script that works for me on a clean install of Jessie is below
#!/bin/bash
# UniPi driver setup
if [ "$EUID" -ne 0 ]
then echo "This script must be run as root"
exit
fi
echo Backup files
cp /boot/config.txt /boot/config.txt.bak
echo Enabling I2C bus...
if ! grep -q '^dtparam=i2c_arm=on' /boot/config.txt
then echo 'dtparam=i2c_arm=on' >> /boot/config.txt
fi
if ! grep -q '^dtparam=i2c_baudrate=400000' /boot/config.txt
then echo 'dtparam=i2c_baudrate=400000' >> /boot/config.txt
fi
echo Enabling the RTC chip...
if ! grep -q '^dtoverlay=i2c-rtc,mcp7941x' /boot/config.txt
then echo 'dtoverlay=i2c-rtc,mcp7941x' >> /boot/config.txt
fi
echo Getting i2c development tools
apt-get install -y i2c-tools
if ! grep -q '^i2c-dev' /etc/modules
then echo 'i2c-dev' >> /etc/modules
fi
echo Removing fake-hwclock...
apt-get purge -y fake-hwclock
update-rc.d -f fake-hwclock remove
apt-get autoremove -y
sed -i '/^if [ -e \/run\/systemd\/system/,/^fi/s/^/#/' /lib/udev/hwclock-set
echo ' '
echo 'UniPi installed.'
echo ' '
echo '!!! REBOOT IS REQUIRED !!!'
echo ' '
read -p "Is it OK to reboot now? [y/N] " -n 1 -r
echo ' '
if [[ $REPLY =~ ^[Yy]$ ]]
then
reboot
else
echo 'Reboot to finish configuring drivers'
fi
echo ' '