Add multiple options support to PBS::Setup::Script:

If a single argument is present like the previous version, it assumes it is
the environment to use. But you can then pass a list of key/value options.

You can even mix the two. Valid uses:

    use PBS::Setup::Script 'my_env';
    use PBS::Setup::Script env => 'my_env', opt1 => 'val1';
    use PBS::Setup::Script 'my_env', opt1 => 'val1';

Signed-off-by: Pedro Melo <melo@simplicidade.org>
Add option chdir_to_root to PBS::Setup::Script

If true, it will chdir() to the project root.

Signed-off-by: Pedro Melo <melo@simplicidade.org>