Print ASnumbers in asplain format and stop using the old asdot format.

Print ASnumbers in asplain format and stop using the old asdot format.
While there clean up some draft comments with their RFC number.
The detection for 4-byte ASPATH attributes is a bit sloppy but since
all resonable BGP versions use 4-byte ASnumbers now we default to them
unless we know it is a 2-byte encoding.
Kill it with fire. deraadt@ & job@ OK sthen@