Remove duplicate file name ToSource.js.
git mv src/outputgeneration/ToSource.js src/outputgeneration/X.js
git mv src/outputgeneration/X.js src/outputgeneration/toSource.js
Mac OSX is case insensitive bug case preserving
Fix issue with '@@iterator' in Firefox.

Since Firefox does not support symbols but they do have iterable
Map and Set implementations, using '@@iterator', our for-of loops
do not work with Firefox.

This adds Symbol.iterator to Map.prototype and Set.prototype

Fixes #1142
Fixes #1144