Add the message= parameter to the null screen driver. (dm)


git-svn-id: svn://mielke.cc/main/brltty@8393 91a5dbb7-01b9-0310-9b5f-b28072856b6e
Fix the localization of the deault no screen message. (dm)


git-svn-id: svn://mielke.cc/main/brltty@8394 91a5dbb7-01b9-0310-9b5f-b28072856b6e