We might avoid some temporaries in putMessagesImpl

We might avoid some temporaries in putMessagesImpl

Summary:
This is folly github pull request https://github.com/facebook/folly/pull/184

It seems we might avoid some temporaries in putMessagesImpl
function. To do so we pass arguments directly to constructors
with the help of emplace_back member.

Test Plan:
All folly/tests, make check for 37 tests, passed.

Signed-off-by: Nicholas Ormrod <njormrod@fb.com>
Reviewed By: davejwatson@fb.com

Subscribers: folly-diffs@, yfeldblum, chalfant

FB internal diff: D1998515

Tasks: 6783581

Signature: t1:1998515:1429207683:056db129405bed212f50a50821f095c8d3694ec8