lib: don't penalize setTimeout() common case

The common case is where setTimeout() is called with two arguments,
the callback and the timeout.  Specifying optional arguments in the
parameter list forces common case calls to go through an arguments
adaptor stack frame.

PR-URL: https://github.com/iojs/io.js/pull/1221


Reviewed-By: Trevor Norris <trev.norris@gmail.com>