add feature detection
add feature detection

aidenzou/shake.js,teazean/shake.js,Larthas/shake.js,alexgibson/shake.js,alexgibson/shake.js,sharp-c/shake.js,Larthas/shake.js,luck2011/shake.js,teazean/shake.js,sugarshin/shake.js,luck2011/shake.js,aidenzou/shake.js,sharp-c/shake.js,sugarshin/shake.js