Fix calc_aheads()
Fix calc_aheads()

The algorithm should use .vote, according to the STV.java that is the
pattern for this code.

Note: this slightly alters the values/progression of .ahead values
 during the processing of an election.
Note: no ASF Board meeting election over the past 16 years is affected.

apache/steve,apache/steve,apache/steve,apache/steve,apache/steve,apache/steve