make write_marked() always call write_file() with nonamechange set to

make write_marked() always call write_file() with nonamechange set to
TRUE (and hence no longer take a namechange parameter itself) to fix a
bug where writing a selection would change the current filename, and
make die_save_file() do the same since we don't need to change the
current filename if we're writing emergency backup files

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@1770 35c25a1d-7b9e-4130-9fde-d3aeb78583b8