fix travis build: builds were failing because libz.so location changed.
Changed dereference.py to keep tuples as tuples
added unit test for dereference patch
ReferenceField query chaining bug fixed.
add myself to AUTHORS
QuerySet chaining test was supplemented with ReferenceField
chaining test
more ordering unit tests
show that order_by followed by limit works, but not the other way around
Don't run unset on IntField if the value is 0 (zero).
Fix the implementation.
Don't run unset on IntField if the value is 0 (zero).

The IntField in unset if the IntField value doesn't validate to "truthify" (therefore, is
set as 0) and the default value of the IntField in question is 0.
This is not a logical functionality in my opinion. Take this example.
You have an IntField that is a counter which can be incremented and
decremented. This counter has the default value of 0 and is a required
field. Every time the counter reaches 0, the field is unset.
Merge pull request #241 from benoitlouy/fixing_travis_build

Fixing travis build
Trying to fix travis
next test
Travis travis travis
Updated pymongo versions and pillow wont work
Fix test_require for Django
Try and fix wobbly test
Merge remote-tracking branch 'origin/pr/254'
Merge remote-tracking branch 'origin/pr/272'