Interactive Install Script for GitLab 6.1 on Ubuntu 12.04/12.10

Here is an interactive script that tries not to make too many assumptions about the install environment and leaves the user the option to install major dependencies in the manner of their choosing.

If the user already has Python, Ruby, Nginx, or MySQL/Postgres installed or would like them installed in a specific way, the script aborts and can be re-run safely.

Many of the repetitive and installation tasks have been factored out, and the software versions are stored as variables.  This should make for simple upgrading in the future.

All options are either chosen interactively or set from command line flags, making it very simple to get up-and-running.  For security reasons, the script will prompt for database passwords when needed.

Many thanks for GitLab!