in do_credits(), display Florian König's name properly in UTF-8 mode;

in do_credits(), display Florian König's name properly in UTF-8 mode;
since we can't dynamically set that element of the array to its UTF-8
equivalent when in UTF-8 mode, we have to use the ISO-8859-1 version and
pass every string in the credits through make_mbstring() to make sure
they're all UTF-8 (sigh)

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@2373 35c25a1d-7b9e-4130-9fde-d3aeb78583b8