handle_wrap: IsRefed() -> HasRef()

Rename slightly to HasRef() at bnoordhuis’ request.
Better reflects what we actually do for this check.

Refs: https://github.com/nodejs/node/pull/6395
Refs: https://github.com/nodejs/node/pull/6204
Refs: https://github.com/nodejs/node/pull/6401
Refs: https://github.com/nodejs/node/pull/6382
Refs: https://github.com/nodejs/node/pull/6381

PR-URL: https://github.com/nodejs/node/pull/6546


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>