Backout 6f5b253ab7b7 - Bug 818843 - This change broke building B2G on the mac. r=me

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extra : rebase_source : 73c82280ee691d4874e0c51c5e90165e92cc40f0
Backout c9831bed6bb7 - Bug 818843 - This change broke building B2G on the mac. r=me

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extra : rebase_source : 7bef8dc1c394d45302f17379ab2cbd90ecda6975
Bug 705371 - [CC] don't add JSContexts that have no children to the cycle collector graph, r=mccr8
Backout e4550612487b & c3008e662841 (bug 827274) for mochitest-chrome crashes on a CLOSED TREE
Bug 811527 - generate_diff.py does not ensure that m-c mirror of mozbase is internally compatible;r=jmaher ; follow-up, DONTBUILD because NPTOB
Added tag FIREFOX_AURORA_20_BASE for changeset 5bb309998e70
Merging in version bump NO BUG