OStatus: save file records for enclosures

Also stripping id from foreign HTML messages (could interfere with UI) and disabled failing attachment popup for a.attachment links that don't have a proper id, so you can click through instead of getting an error.

Issues:
* any other links aren't marked and saved
* inconsistent behavior between local and remote attachments (local displays in lightbox, remote doesn't)
* if the enclosure'd object isn't referenced in the content, you won't be offered a link to it in our UI

js/util.js

@@ -423,8 +423,11 @@ var SN = { // StatusNet
             };
 
             notice.find('a.attachment').click(function() {
-                $().jOverlay({url: $('address .url')[0].href+'attachment/' + ($(this).attr('id').substring('attachment'.length + 1)) + '/ajax'});
-                return false;
+                var attachId = ($(this).attr('id').substring('attachment'.length + 1));
+                if (attachId) {
+                    $().jOverlay({url: $('address .url')[0].href+'attachment/' + attachId + '/ajax'});
+                    return false;
+                }
             });
 
             if ($('#shownotice').length == 0) {