#189 Using external editor doesn't update preview or index

[Anonymous]

Using external_editor doesn't update the preview and
the index for the file.
The problem is that external_editor modifies the file
field using a PUT to the file field url, so the update
will go directly to the file (the real method called is
the PUT one of OFS.Image) and AttachmentField has no
means to know that the file has been updated.
See also
http://thread.gmane.org/gmane.comp.web.zope.plone.user/42115

(I don't have an sf account, my email is luca at wetron
dot es)