Does not purge image scales upon Editing due to patched ___<lang>___ URL scheme

[jnachtigall]

plone.app.caching purges ImageFields with https://github.com/plone/plone.app.caching/blob/master/plone/app/caching/purge.py#L179:

                if IImageField.providedBy(field):
                    for size in field.getAvailableSizes(self.context).keys():
                        yield "%s_%s" % (fieldURL, size,)

That is, when I have a news item with an image included and I change it, then all available scale sizes of this image are purged on the caching proxy (e.g. varnish). With raptus.multilanguagefields this does not work anymore, because the image scale is patched to be "image______scale". I think this is done in https://github.com/Raptus/raptus.multilanguagefields/blob/master/raptus/multilanguagefields/patches/imaging.py#L52

To fix one would just need to copy https://github.com/plone/plone.app.caching/blob/master/plone/app/caching/purge.py over to raptus.multilanguagefields and to register and adjust it accordingly.

[jnachtigall]

How it could be done:
http://stackoverflow.com/questions/20588907/updating-attached-image-of-news-item-does-not-purge-scaled-image-from-varnish-bu/21050051?iemail=1&noredirect=1#21050051