l10n: de.po: translate 5 new messages

Translate 5 new messages came from git.pot update in 235537a
(l10n: git.pot: v1.8.2 round 3 (5 new)).

Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com>
Acked-by: Thomas Rast <trast@inf.ethz.ch>