fold unnecessary make_fold_req2/4 into make_fold_req/4
fold unnecessary make_fold_req2/4 into make_fold_req/4

also renamed make_fold_req3 to make_fold_reqv, since the 3 didn't make
sense any more, but it's still nice to have the name slightly different
than the exported functions

also fix a bit of doc

Kyorai/riak_core