Carrier trait for testing, DON'T LAND#35056

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nrc wants to merge 4 commits intorust-lang:masterfrom

Commits on Aug 8, 2016

Use a Carrier trait with the `?` operator
Nick Cameron
committed
Expand try! to ? breaking change - DO NOT LAND!
Nick Cameron
committed

Commits on Aug 9, 2016

Fixes
Nick Cameron
committed
Remove the Option and bool impls for carrier and add a dummy impl
Nick Cameron
committed