Summary: This adds local type for each FiberManager. Only local of given type can be created on fibers of this FiberManager. Locals of other types will be just treated as regualar thread-locals.

Test Plan: unit test

Reviewed By: bwatling@fb.com

Subscribers: folly-diffs@, yfeldblum, chalfant

FB internal diff: D1969739

Signature: t1:1969739:1428345931:aff5deb526c179158e5881b29330ff3f6698149a