Use Couchstore for initial build

Instead of using Erlang to build the initial index bottom up, use the
C based initial index build from Couchstore.

Change-Id: Ie639763a59fadb31c48fc4a0ec3ab66d87918a18
Reviewed-on: http://review.couchbase.org/40142
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Volker Mische <volker.mische@gmail.com>