Summary:
The `collectAll()`, `collectAllRange()` and `collectAllWindowed()` functions now cancel their subtasks when either the parent task is cancelled or when any of the subtasks fail with an exception.

The `collectAllTry()`, `collectAllTryRange()` and `collectAllTryWindowed()` functions now cancel their subtasks if the parent task is cancelled, but not if the child tasks fail with an exception.

The logic between the distinction here is that if you are calling one of the 'try' functions then you are intending to handle partial failure and so probably want each of the operations to run to completion independently of the others.

Reviewed By: kirkshoop

Differential Revision: D16820619

fbshipit-source-id: 5c203b41592a0145ff7be1c609dfccd39c41a3df