Adding item_frequencies_mr so as to not rely on exec.
Fixing inline map reduce to not store results in a collection. This requires pymongo's collection.inline_map_reduce.
Merge branch 'dev' of http://github.com/samuelclay/mongoengine into dev

Conflicts:
	mongoengine/queryset.py
Merge branch 'dev' of https://github.com/hmarr/mongoengine into dev

* 'dev' of https://github.com/hmarr/mongoengine: (37 commits)
  Now Raise an exception if subclasses are missing at querytime.
  Added choices note to upgrade docs
  Improved update in test case for removing inheritance
  Updated changelog and authors
  remove keep_temp from map_reduce
  Removed keeptemp from map_reduce as 0.5 requires pymongo 1.11
  Remove old pymongo version checks
  Added version check to the polygon test to ensure server version >= 1.9
  Commas help too :)
  left some conflict markers in - oops
  Added tests for polygon queries
  Updated upgrade.rst
  more tests for embedded lists
  Added tests for showing how to set embedded document indexes
  Updated changelog
  Updated changelog
  prefer to use map-reduce to db.eval where possible
  Updated AUTHORS
  Finishing touches to where implementation - thanks to dcrosta
  docstring for `where()`
  ...
Merge branch 'dev' of github.com:samuelclay/mongoengine into dev

* 'dev' of github.com:samuelclay/mongoengine: (126 commits)
  Popping out replicaSet if not being used.
  Adding support for ReplicaSetConnection (in pymongo v2.1)
  Updated connection - so handles < pymongo 2.1
  Updated connection for pymongo 2.1 support
  added custom db_alias support for MongoEngine DjangoSession
  Added David to Authors
  Abstract documents can now declare indexes
  Updated docs and Authors list re: db_alias
  Syntax cleaning
  Fixing test
  Added some tests  #384
  db_alias using in model, queryset, reference fields, derefrence.
  Dynamic Documents now support string query lookups
  Added test showing you can add index for dynamic docs
  Added Jan to the contributors list
  Fixed GridFS documents can now be pickled
  Multiple fields with the same db_field now raises Exception
  Updated Docs and bumped version
  Updated with_id to raise Error if used with a filter.
  Added ReferencField handling with .distinct()
  ...