* mu-msg: add mu_msg_close_file_backend

src/mu-msg.h

@@ -69,6 +69,18 @@ MuMsg *mu_msg_new_from_doc (XapianDocument* doc, GError **err)
 	G_GNUC_MALLOC G_GNUC_WARN_UNUSED_RESULT;
 
 
+/**
+ * close the file-backend, if any; this function is for the use case
+ * where you have a large amount of messages where you need some
+ * file-backed field (body or attachments). If you don't close the
+ * file-backend after retrieving the desired field, you'd quickly run
+ * out of file descriptors. If this message does not have a
+ * file-backend, do nothing.
+ *
+ * @param msg a message object
+ */
+void mu_msg_close_file_backend (MuMsg *msg);
+
 /**
  * increase the reference count for this message
  *