[1268] Changes for ckan 2.2.
[1229] Validation errors when sysadmin edits Pub Hub or harvested dataset - fix also requires CKAN #1400 commit.
[noticket] No real change - just PEP8 and CKAN style imports.
Merge branch '1268-ckan-2.2'

Conflicts:
	ckanext/dgu/forms/dataset_form.py
	ckanext/dgu/plugin.py