CLJS-1114: browser REPL script loading race condition
CLJS-1114: browser REPL script loading race condition

the browser REPL cannot use document.write to load scripts after
page load as that would blow away the document.

However appending script element to document.body suffers from
race conditions due to asynchronous script loading when not
using document.write.

Add a load queue which enforces sequential load order.

mstang/clojurescript,mstang/clojurescript,mstang/clojurescript