events: optimize listener array cloning

This both switches to a single algorithm for array cloning and also
speeds up (by ~100% in the ee-listeners-many benchmark) the
"many elements"  case that was previously handled by
`array.slice()`.

PR-URL: https://github.com/iojs/io.js/pull/1050


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Julian Duque <julianduquej@gmail.com>