Ignore empty batches instead of sending invalid CQL to Cassandra.
Allow multiple ORDER BY conditions to be set.

Supports both .order_by('foo', 'bar') and chained .order_by() calls.
Added a derived Date type.

Internally it is stored as a timestamp but the value is
exposed as a  instance.
Merge pull request #35 from dokai/empty-batch

Ignore empty batches instead of sending invalid CQL to Cassandra.
Merge branch 'multiple-order-by' of github.com:dokai/cqlengine into dokai-multiple-order-by

Conflicts:
	cqlengine/query.py
adding test around chaining order_by statements
Merge pull request #37 from dokai/date-column

Added a derived Date type.
making date deserialize with utc timezone
modifying pk comparison to look at the db_field_name, so it's not dependent on the ids being identical
Merge remote-tracking branch 'upstream/master'

Conflicts:
	cqlengine/columns.py
	cqlengine/query.py