Ice install script for Amazon Linux AMI (bash)

Add an installation script that downloads+installs Grails,
and downloads+configures Ice. To bootstrap, the user need only download
the installation script onto their Amazon Linux AMI -- the script takes
care of installing git and fetching the Ice repository.
Check in the correct install.sh

Previous install.sh was not the final version; this version checks for
existing files, and generally behaves nice if you call it multiple times
or from different directories.
Merge pull request #18 from Travis-Snoozy/master

Ice install script for Amazon Linux AMI (bash)
Thanks Travis for the contribution. I didn't test this script myself. Maybe someone else can test it.