fix previous commit causing errors for serializers with source='*'
merge in an updated version of my old writable-dotted-field-source branch ( see PR tomchristie/django-rest-framework#1052 )
incorporate in changes from @jacobg's monkeypatch at https://gist.github.com/jacobg/7587826
use _get_source_value one more place
Merge branch 'fix-dotted-writable-fk-source' into kx

Conflicts:
	rest_framework/serializers.py