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
config: teach "git -c" to recognize an empty string

In a config file, you can do:

  [foo]
  bar

to turn the "foo.bar" boolean flag on, and you can do:

  [foo]
  bar=

to set "foo.bar" to the empty string. However, git's "-c"
parameter treats both:

  git -c foo.bar

and

  git -c foo.bar=

as the boolean flag, and there is no way to set a variable
to the empty string. This patch enables the latter form to
do that.