update changelog and some improvements.
Fix test suite...
Trigger Travis
typo
Now images are traversed to the original object if there isn't a local image loaded into the tile.
update changelog and some improvements.
Fix test suite...
Trigger Travis
typo
Now images are traversed to the original object if there isn't a local image loaded into the tile.
Merge branch 'issue_158' of github.com:collective/collective.cover into issue_158

Conflicts:
	docs/HISTORY.rst
Purge cache when changing images.
Implements IPurgePaths for cover tiles, this code should be moved to plone.tiles to implement it for every persitent tile.
Merge pull request #159 from collective/issue_158

closes #158