Add ConcurrentHashMap installable
Add ConcurrentHashMap installable

Summary:
ConcurrentHashMap is a newly added feature and we wanted to test it in our enviornment, making it installable.

Built & Installed on ubuntu 14 env.
Closes https://github.com/facebook/folly/pull/659

Reviewed By: djwatson

Differential Revision: D5629159

Pulled By: yfeldblum

fbshipit-source-id: 8a40e768f3db7918a3b284059f2efa0b7ecb9aca

Orvid/folly,facebook/folly,rklabs/folly,facebook/folly,facebook/folly,Orvid/folly,Orvid/folly,rklabs/folly,rklabs/folly,Orvid/folly,rklabs/folly,Orvid/folly,facebook/folly,rklabs/folly,facebook/folly