Install go 1.1.1 rather than 1.1
The argument to printf is mandatory in some shells, so use empty string
Allow location of where to install Go to be overridden
Escape dollars when writing to .profile or /etc/profile
Update documentation

- Behaviour of $PREFIX
- Behaviour when not run as root
Actually exit if Mercurial is not found
Don't run sudo because script will work when not run as root