Add header aliasing vbucket functions to shorter names

Change-Id: I874c0fc4c09535aab5eb67dd51a9bd4fbbd0bd6c
Reviewed-on: http://review.couchbase.org/34597
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>