SERVER-14138 mongos incorrectly targets multiple shards for nested field shard keys
(cherry picked from commit 777de742ee578b62b12ded8381aadf98dfa9fa5f)

Conflicts:
	jstests/sharding/hash_regex_targetting.js
SERVER-14180 fix double free in access planning for $elemMatch

(cherry picked from commit 2453cec627bb8f6100980dea273ac9eb54ecd645)
SERVER-14176 query planner should obey $natural sort

(cherry picked from commit 89383b224f061d306240d621745ba082a4ecb23b)
SERVER-14138 fix shard key targeting tests backported from v2.7
Merge remote-tracking branch 'upstream/v2.6' into v2.6