Update future branch descriptions

docs/FUTURE.md

@@ -29,8 +29,6 @@ There is some work required before LevelEd could be considered production ready:
 
 - Introduction of property-based testing.
 
-- Riak modifications to support the optimised Key/Clock scanning for hashtree rebuilds.
-
 - Amend compaction scheduling to ensure that all vnodes do not try to concurrently compact during a single window.
 
 - Improved handling of corrupted files.
@@ -117,3 +115,15 @@ This branch changes the behaviour slightly at the non-coordinating vnodes.  Thes
 This should save two object fetches (where n=3) in most circumstances.
 
 Note, although the branch name refers to the put fsm - the actual fsm is unchanged by this, all of the changes are within vnode_put
+
+### AAE Rebuild Acceleration
+
+Branch: [mas-leveled-scanner-i649](https://github.com/martinsumner/riak_kv/tree/mas-leveled-scanner-i649)
+
+Branched-From: [mas-leveled-putfsm](https://github.com/martinsumner/riak_kv/tree/mas-leveled-putfsm)
+
+Description:
+
+The riak_kv_sweeper which is part of the post-2.2 develop branch controls folds over objects so that multiple functions can be applied to a single fold.  The only aspect of the Riak system that uses this feature at present is AAE hashtree rebuilds.
+
+This branch modifies the kv_sweeper so that if the capability exists, and unless a sweeper has explicitly stated a requirement not to allow this feature, the sweeper can defer the fetching of the objects.  This means that the sweeper will fold over the "heads" of the objects returning a specially crafter Riak Object which contains a reference to the body rather than the actual body - so that the object body can be fetched if and only if access to the object contents is requested via the riak_object module.