Introduce "obligation forest" data structure into fulfillment to track backtraces#30533

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bors merged 13 commits intorust-lang:masterfrom

nikomatsakis:fulfillment-tree

Jan 16, 2016

Commits on Jan 14, 2016

modify trait checker to track the variables on which trait resolution is
nikomatsakis
committed
implement the obligation forest data structure and add some unit tests
nikomatsakis
committed
switch the fulfillment context to use the new obligation forest;
nikomatsakis
committed

Commits on Jan 16, 2016