Make inheritance of children work correctly
Merge pull request #5 from MITx/mitx-tweaks

Make inheritance of children work correctly
Add a  method to the KeyValueStore interface for checking whether a key exists already
Merge pull request #6 from MITx/cale/kvs-has

Add a  method to the KeyValueStore interface for checking whether a key ...
Make DbModel __contains__ return False for keys that it knows nothing about
Merge pull request #7 from MITx/cale/kvs-has

Make DbModel __contains__ return False for keys that it knows nothing ab...
Make fields hashable and comparable based on name and sequence
Add function to retrieve serialized value from model using a field
Don't put a field on an object multiple times because of inheritance
Make Object and List primitives generate new lists and dictionaries as defaults
Add tests for safe field defaults
Make inheritance of fields from mixin classes work correctly
Use inspect module to get all inherited member fields
Merge remote-tracking branch 'mitx/master'

Conflicts:
	xblock/test/test_runtime.py