py-django-extensions: updated to 2.1.3

2.1.3:
Fix: Readme, add direct linkt to screencast video
Fix: graph_models, regression under Python 2
Fix: ForeignKeyAutocompleteAdmin, 2.0.8 breaks ForeignKeyAutocompleteAdmin
Fix: AutoSlugField, fix regression when copying an autoslug model require the explicit clearing of the slug if it needs to be recalculated
Fix: technical_response, check for AttributeError
Improvement: graph_models, Add feature disable_abstract_fields
Improvement: AutoSlugField, Add overwrite_on_add
Improvement: runscript, Improve module existence test in runscript

(adam)