Bug 988821 - Move minor GC into main GC loop, r=terrence

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extra : rebase_source : 3478c0b5110c9891b3bb1ea2bccdc63954d359fd
Bug 619558 - Enable generational GC on desktop; r=sfink, sr=naveed

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extra : rebase_source : 7234cc03ed04d48d54ac613e25708a1321501f24