MB-23319: Skip segment if search key < startKey
MB-23319: Skip segment if search key < startKey

This results in a 4X speed up for Gets & Iterations..
Iterating 9000000 items took 40519ms
vs
Iterating 9000000 items took 10751ms

Change-Id: Ifc5214bd00c40f5e1a62fd9b0fa16a576d0a5342
Reviewed-on: http://review.couchbase.org/80607
Reviewed-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>
Tested-by: Sundararaman Sridharan <333a3f71d3ad6e01fc953c4fa06bc1f3cd014910@couchbase.com>

couchbaselabs/moss,steveyen/moss,steveyen/moss