Use async waits for beep durations to prevent the loss of USB key events on some devices. (dm)


git-svn-id: svn://mielke.cc/main/brltty@8232 91a5dbb7-01b9-0310-9b5f-b28072856b6e
Another approximateDelay() to asyncWait() conversion. (dm)


git-svn-id: svn://mielke.cc/main/brltty@8233 91a5dbb7-01b9-0310-9b5f-b28072856b6e