2i improvements added in 1.4.4-1.4.6

* Add 2i term regex filter
* Make 2i pagination sort optional
* Use sext NIF (C implementation)
* Fix vnode sending > max_results items for 2i query
* Add 2i AAE command
* Fix some mixed cluster queries (1.3.x and 1.4.2)
* Make memory backend obey 2i return terms properly
Fix bug with stats for legacy counters.

With legacy counters, the operation sent to the vnode is simply an
integer increment, not a `crdt_op` record.
Merge pull request #778 from basho/bugfix/sdc/legacy-counter-stat-error

Fix bug with stats for legacy counters.
Merge pull request #776 from basho/feature/2i-1.4.4

2i improvements added in 1.4.4-1.4.6
Merge remote-tracking branch 'origin/develop' into feature/pevm-metadata-cache.merged

Conflicts:
	src/riak_object.erl
address review comments