Bug 1011355 (part 1) - Remove FreeList::allocateFromNewArena(). r=billm.

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extra : rebase_source : 0098da34802c9febdd0fe351859ce995ba7e449a
Bug 1011355 (part 2) - Add a CompactFreeSpan class. r=billm.

--HG--
extra : rebase_source : 693f7ff5abb5e3335b62c790c997f713526027f0
Bug 1011355 (part 3) - Tiny FreeSpan tweaks. r=billm.

--HG--
extra : rebase_source : 739e5104bee8ea878d5c8e421d7cd6cfd095c2da