Attempt to increase usefulness of LOGERROR msg :)

This is an attempt to increase the usefulness of this specific log message.  We attempt to create a tmpfile using mkstemp and if this fails then we state we are unable to create a digest file.  If it fails, then *for some reason* we are unable to write to /tmp.  This will at least help the user understand the action we are trying to take, they can then find out why it is failing themselves (by checking available space, perms, file descriptor limits etc.).