Fixed sum and average mapreduce function for issue #375
Merge branch 'master' of https://github.com/MongoEngine/mongoengine

Conflicts:
	AUTHORS
Fixed sum and average queryset function

* Fixed sum and average map reduce functions for sum and average so that
        it works with mongo dot notation.

* Added unittest cases / updated them for the new changes
Added a get_proxy_obj method to FileField and handle FileFields in container fields properly in ImageGridFsProxy.
Fix crash on Python 3.x and Django >= 1.5
extending support for queryset.sum and queryset.average methods
Merge pull request #392 from lig/patch-1

Fix crash on Python 3.x and Django >= 1.5
Prep for django and py3 support
Merge remote-tracking branch 'origin/pr/392' into 392
Added Django 1.5 PY3 support (#392)
Fixed ListField setslice and delslice dirty tracking (#390)
Merge branch 'master' of github.com:MongoEngine/mongoengine
_dynamic field updates - fixed pickling and creation order

Dynamic fields are ordered based on creation and stored in _fields_ordered (#396)
Fixed pickling dynamic documents `_dynamic_fields` (#387)
Reload uses shard_key if applicable (#384)
Document.select_related() now respects `db_alias` (#377)
Fixed as_pymongo to return the id (#386)
Merge remote-tracking branch 'origin/pr/376'

Conflicts:
	AUTHORS
Fixed sum and average mapreduce dot notation support (#375, #376)
Update fields.py

Typo in documentation for DecimalField
Merge remote-tracking branch 'origin/pr/391' into 391