Enhancement of content type "List of related terms" (term_list)

Problem/Motivation

It would be nice to be able to list terms including the one that is used as base to fetch the list.
This is especially handy for theming purposes since you'll get a single list element.

Proposed resolution

The attached patch adds a new configuration option (absolutely backward compatible!) and allows you to configure for the child / parent type that the current term should be included in the list.

Remaining tasks

Reviews needed.

User interface changes

New checkbox in the settings form that only shows up if the type child / parent is selected.

API changes

None