Issue #1014086 by catch, nod_, martin107, quietone, dww, mariacha1, Spokje,...

Issue #1014086 by catch, nod_, martin107, quietone, dww, mariacha1, Spokje, yogeshmpawar, pounard, Wim Leers, mfer, mikeytown2, mbutcher, moshe weitzman, Fabianx, borisson_, alexpott, donquixote, sun, andypost, dawehner: Stampedes and cold cache performance issues with css/js aggregation