Return tombstones (Vclock) so a K/V can be rewritten directly after a de...

Recently an item came up on the mailing list with the subject: "Quickly deleting + recreating item in Riak deletes new item"

Turns out this or something very much related was discussed earlier:
http://lists.basho.com/pipermail/riak-users_lists.basho.com/2011-June/004601.html

As suggested by Andrew Thompson here:
http://lists.basho.com/pipermail/riak-users_lists.basho.com/2013-July/012520.html

this pull request sets 'deletedvclock' and returns the Vclock for tombstones / items that were deleted very recently.