CHANGING its mind for the second successive time on the same issue the Manitoba legislature decided Thursday by a decisive majority to impose a !50-mile-an-hour daytime speed limit for motor vehicles on the province’s highways.A third of the members of the House participated in the spirited debate that preceded reinstatement of the speedI M . • i.™ . A .... 4 ^ ^ ~ ^ ■» A T • ftA * 1 a. • ^ *Highway SpeedLimited To 50.L.A.'s Again Change Mind;Plan To Curb Fast Motorists