[ppml] proposal 2007-20

I would like to withdraw my 2007-20 from consideration. If the community
finds parts of it useful I recommend incorporating them into one of the
other proposals up for consideration (perhaps 2007-25).

2007-25 already addresses one of the issues (200 /48 -> 200 separate
customers).  A definition of what exactly an "existing ISP" is might
still be useful.

- Kevin