Assume that the global configuration (~/.darcs/author) contains more
than author. This is handy if you use different names and mail addresses
for repositories, e.g. to distinguish between work and private, or one
mail address per project.
When a new repository is created, darcs shows a selection of the
available author names. After choosing one, darcs overwrites the global
configuration (~/.darcs/author) with the selected author name.
When the global configuration contains more than one author, the name
should instead be stored in the repository-local confoguration
(_darcs/prefs/author). This way, darcs can prompt again when the next
repository is created.