MB-19652: Save 24 bytes per index btree block when READ_TREE is disabled
MB-19652: Save 24 bytes per index btree block when READ_TREE is disabled

Change-Id: Iec8feba87bd7f5fb5c1b523cfd52ed3f5a277546
Reviewed-on: http://review.couchbase.org/66159
Reviewed-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>
Tested-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>

hisundar/forestdb,wurikiji/forestdb,couchbase/forestdb,hisundar/forestdb,wurikiji/forestdb,couchbase/forestdb