l10n: de.po: translate 38 new messages

Translate 38 new messages came from git.pot update in fe05e19
(l10n: git.pot: v2.1.0 round 1 (38 new, 9 removed)).

Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com>
po/TEAMS: add new members to German translation team

Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com>
Merge git://github.com/git-l10n/git-po

* git://github.com/git-l10n/git-po:
  po/TEAMS: add new members to German translation team
  l10n: de.po: translate 38 new messages
tree-walk: be more specific about corrupt tree errors

When the tree-walker runs into an error, it just calls
die(), and the message is always "corrupt tree file".
However, we are actually covering several cases here; let's
give the user a hint about what happened.

Let's also avoid using the word "corrupt", which makes it
seem like the data bit-rotted on disk. Our sha1 check would
already have found that. These errors are ones of data that
is malformed in the first place.