Revert "use array contains everywhere"

This reverts commit c1ca9d66a95b4991ddcc0bba1a6a5010eb4dc042.
advanced xhr controller: request({advanced: fn})
Object.assign ignores null and undef source args

August 24, 2014 Draft Rev 27
http://wiki.ecmascript.org/doku.php?id=harmony:specification_drafts
find/findIndex no longer ignore array item holes

August 24, 2014 Draft Rev 27
http://wiki.ecmascript.org/doku.php?id=harmony:specification_drafts
build 0.6.1
build 0.6.1