Some PEP8 cosmetics and minor readability enhancements.
Ensure the options dictionary include the configuration file.

Moving this to the instance creation makes it easy to use this value
anywhere later on.
Factor out the installation of scripts into a separate function.
Ensure buildout has information about dependencies on every run.

For this we need to call the installation of scripts and extra eggs on
every run, i.e.: during update as well as install. Without this,
supervisor and the eggs listed in the plugins option will appear and
disappear from the picked eggs list, e.g.: they appear on first run,
but are removed on subsequent runs, unless you manually trigger
another install of the part.
Update the package history.
Merge pull request #2 from collective/picked-eggs-dissapearance-fix

Picked eggs dissapearance fix.