Set rebar.config deps back to 2.0 branches
Allow handoff sender to abort handoff by throw'ing from fold fun

There's no reason why the handoff sender fold fun has to continue
folding when there's a TCP error.  Instead, throw the #ho_acc{}
record with its error={error,Reason} field intact.

If we force the handoff receiver to exit (using exit(HO_pid, kill)),
then we simply see the following logged on the sender side:

    2014-03-17 15:53:30.949 [error] <0.27207.2>@riak_core_handoff_sender:start_fold:266 hinted_handoff transfer of riak_kv_vnode from 'dev1@127.0.0.1' 1415829711164312202009819681693899175291684651008 to 'dev2@127.0.0.1' 1415829711164312202009819681693899175291684651008 failed because of closed
    2014-03-17 15:53:30.950 [error] <0.220.0>@riak_core_handoff_manager:handle_info:289 An outbound handoff of partition riak_kv_vnode 1415829711164312202009819681693899175291684651008 was terminated for reason: {shutdown,{error,closed}}

Also, change the lager:info() message when the handoff receiver
gets a tcp_error message that *includes* the reason and
distiguishes itself from other handoff receiver log messages.

Also, one whitespace correction.
Merge pull request #626 from basho/bugfix/cherrypick/handoff-fold-abort-early-2.0

Allow handoff sender to abort handoff by throw'ing from fold fun

Reviewed-by: andrewjstone
Handoff sender sends sync periodically
Merge pull request #627 from basho/feature/handoff-sender-sync-tick20-rebased

Handoff sender sends sync periodically

Reviewed-by: kellymclaughlin
Add breadth-first AAE exchange

This commit ports the breath-first exchange algorithm from the
synctree code in riak_ensemble to the hashtree code here in riak_core.
This level-by-level exchange is necessary to support streaming and/or
pipelined AAE exchange -- an approach that will soon underpin the new
AAE-based fullsync replication protocol in Riak.
Merge pull request #629 from basho/feature/aae-exchange-bfs-2.0


Reviewed-by: jonmeredith
Crash the caller when you fail to open a file, too
Add comment describing the slight semantic change
Merge pull request #646 from basho/rdb/gh-kv679

Tell the caller when you fail to open a file, too

Reviewed-by: russelldb
Introduce exometer metrics into 2.0
Merge pull request #650 from basho/feuerlabs-exometer5

Introduce exometer metrics into 2.0

Reviewed-by: jburwell
Remove afunix from EXOMETER_PACKAGES.
Afunix is not used at this time, and may cause build issues on some
platforms.
Merge pull request #654 from basho/uw-remove-afunix

Remove afunix from EXOMETER_PACKAGES.

Reviewed-by: jburwell
add skipped_read_repairs to legacy stat map
Merge pull request #655 from basho/uw-add-skipped-repairs-stat

add skipped_read_repairs to legacy stat map

Reviewed-by: jburwell
Update tools.mk to 0.5.6
Fix edoc error in dvvset.erl

Remove use of `@title` tag in module.

From the [Edoc User's Guide
0.7.13](http://www.erlang.org/doc/apps/edoc/chapter.html): Specifies a
title for the overview page. This tag can _only_ be used in an overview
file. The content can be arbitrary text.
Fix `` quoting to `' for Edoc
Don't use @doc tag for -callback

Edoc complains and fails to build the file. Unfortunately, putting the
comment below or above the `-callback` doesn't get it to show up in the
html. But this at least allows it to succeed.