gitlib-s3 smoke tests use environment variables

[This change](https://github.com/fpco/gitlib/commit/0b7f3064fb34dff6029f40335ffaf881480bb746#L8R29) seems to have broken the gitlib-s3 smoke tests: .  This pull request undoes that change and also makes it build with HP 2012.4 (which doesn't have `System.Environment.lookupEnv`).