Optimize js->clj by switching to transients

fixed https://github.com/clojure/clojurescript/commit/e173e54de9de5174601a35d22b8da33096af39d3

Thomas Spellman's patch rebased on current master.

js-to-clj-using-transients.patch no longer applies.

Added a patch, "js-to-clj-using-transients.patch", on Oct 16, 2016 that supersedes "use-transducers-in-js-to-clj.patch" from Aug, 2014. This patch changes cljs.core/js->clj to use transients. Also included is a change to both js->clj and clj->js to use gobject/get and gobject/set instead of aget and aset on JS object.

The JSperf shows a 17% speed improvement in Chrome on the first run, but about equal on the second run: https://jsperf.com/js-clj-transient-perf-test

The code for the JSperf is here: https://gist.github.com/thos37/41c0b38bea3270988a3275332686ab49

What would be the ideal test data for this?

Rohit good catch. Yes that should be changed.