Added staging file previews support

3rd_party_apps/filetransfers/backends/xsendfile.py

@@ -0,0 +1,12 @@
+from django.http import HttpResponse
+from django.utils.encoding import smart_str
+
+def serve_file(request, file, save_as, content_type, **kwargs):
+    """Lets the web server serve the file using the X-Sendfile extension"""
+    response = HttpResponse(content_type=content_type)
+    response['X-Sendfile'] = file.path
+    if save_as:
+        response['Content-Disposition'] = smart_str(u'attachment; filename=%s' % save_as)
+    if file.size is not None:
+        response['Content-Length'] = file.size
+    return response