Use interactive bash by default

Squashed commit of the following:

commit 60bd342bee103dbdb001421be2626b432f79df2c
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue May 6 09:19:51 2014 +0200

    Use interactive shell (and inherit env vars)

commit 09d55ed942b97ebee602d6b995da9d9b7f407427
Author: Thomas Schank <DrTom@schank.ch>
Date:   Mon May 5 08:46:31 2014 +0200

    Use interactive login shell by default; but do not inherit variables