util: fix constructor/instanceof checks

These new checks are similar to the one introduced in 089d6886,
but for other types of objects. Specifically, if an object was
created in a different context, the constructor object will not be
the same as the constructor object in the current context, so we
have to compare constructor names instead.

PR-URL: https://github.com/nodejs/node/pull/3385


Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>