txt and caa rr strings might contain binary control characters
such as newlines and double quotes which mess up the output
in ndb(6) format.
so handle them as binary blobs internally and escape special
characters as \DDD where D is a octal digit when printing.
txtrr() will unescape them when reading into internal
binary representation.
remove the undocumented nullrr ndb attribute parsing code.
5de1f3d9cf