+/* Find or create a directory document.
+ *
+ * 'path' should be a path relative to the path of 'database', or else
+ * should be an absolute path with initial components that match the
+ * path of 'database'.
+ *
+ * If (flags & NOTMUCH_FIND_CREATE), then the directory document will
+ * be created if it does not exist. Otherwise, if the directory
+ * document does not exist, *status_ret is set to
+ * NOTMUCH_STATUS_SUCCESS and this returns NULL.
+ */