events: optimize listener array cloning
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 <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>
Reviewed-By: Julian Duque <6b79c807f33c79ce9edd01e7fc5cbf832e85609c@gmail.com>

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