[EM] Covering , Ranked Pairs, Beatpath, and River

[fsimmons at pcc.edu]

If we measure defeat strength of A over B, primarily by whether or not A covers B, and secondarily by 
the number of winning votes, we get new versions of Ranked Pairs, River, and Beatpath.  These new 
versions retain all of the best properties of their winning votes versions, while always electing uncovered 
alternatives.

In particular, the winner of Ranked Pairs (Covering, wv) goes like this:

1.  Lock the covering relation.

2.  Continue locking in defeats as in ordinary RP(wv).

Note that step one cannot introduce a cycle, because the covering relation is a partial order.