cms.utils.is_valid_page_slug check slug against unpublished titles and when no page has been saved yet, to avoid duplicate slugs at all
Fix PagesTestCase.test_slug_collision for new slug-checking semantic
Remove filter on PUBLISHER_STATE_DELETE
PUBLISHER_STATE_DELETE is not in use anymore
Merge pull request #2492 from yakky/feature/unique_slug

Slug uniqueness
Merge pull request #2501 from yakky/feature/remove_publisher_state_delete

PUBLISHER_STATE_DELETE is not in use anymore
Merge branch 'develop' into language_publish3

Conflicts:
	cms/models/pagemodel.py
	cms/utils/page.py