+ "Evaluate BODY with progress message and return its value.
+SPEC is a list as followed (LABEL TOTAL [VAR]).
+LABEL is an identifier what is specidied by `elmo-progress-notify'.
+If TOTAL is nil, the first `elmo-progress-notify' call must be
+with a `:total' parameter.
+If optional parameter VAR is specified, bind it with a progress counter object.
+MESSAGE is a doing part of progress message."