4 4 x

These changes were spurred by a failed attempt to install manually in an Ubuntu 14.04 VM. My initial run of xtuple/scripts/install_xtuple.sh reported success ("xtuple > All Done!") when in fact there had been a large number of errors. The changes to install_xtuple.sh allow it to "fail fast" but still run through the whole script for debugging purposes (-k). The tweaks to the README emphasize using Vagrant to reduce the likelihood of running into the problems I had.