Issue #2946 by chx, michaellenahan, jcnventura, quietone, ifrik, wengerk,...

Issue #2946 by chx, michaellenahan, jcnventura, quietone, ifrik, wengerk, AaronBauman, salvis, pplantinga, sun, David_Rothstein, tatarbj, alexpott, Wim Leers, iMiksu, vijaycs85, anoopjohn, nedjo, Owen Barton, bjaspan, soxofaan, Gogowitsch, raman.b, robeano, deepakrmklm, bleen, xmacinfo, catch, beginner, dww, Gábor Hojtsy, webchick, Dries, larowlan, snufkin, RobRoy, bdragon, wizonesolutions, Lendude, sokru: Login fails and no warning is issued if cookies are not enabled