Bug 1064578 - Sweep tables in parallel; r=jonco r=bhackett

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extra : rebase_source : f4e1d6c1067c2ae5c01f62dee3d4b28471c62e98
Bug 1074961 - Part 1: use more generic names for the members of ChunkPool; r=sfink

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extra : rebase_source : c44d91125cf48e7f34fb92cd04670bac9247b0c2
Bug 1074961 - Part 2: change the name of chunkPool to be more descriptive; r=sfink

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extra : rebase_source : 2a6319591731c2d46f12ac749f8e1f69d50762c5