Summary:
This diff fixes various issues with memonger, and works at leasrt with rbgirshick's failure case, Resnet-50, and new harder unit test. I will still create a proper resnet50-test.
1) Introduce concept of "tokens". These are passed down the dependency chains, and a blob can be used for recycling only if it owns all the tokens that are currently in possession. Tokens are added when branching, and tokens are redeemed after all inputs are satisfied. A bit hard to explain.
2) There were various bugs due to bad code: the free_blobs data structure is of different type when we have blob sizes and when we haven't. I plan to rewrite this soon. But there were some bugs.
3) Added a harder unit test that failed before.
4) Added test for resnet50 + memonger
Reviewed By: asaadaldien
Differential Revision: D5193393
fbshipit-source-id: bc2a714877aa1201c32a5ba8ade862865e455711
