Compatibility with phonegap 2.0 (Cordova)

The change made gets the plugin working with phonegap 2.0
Merge pull request #987 from aetchegoyen/patch-1

Compatibility with phonegap 2.0 (Cordova)
BarcodeScanner: align JS with cordova.require
Add ZXing 2.1
Merge pull request #3 from phonegap/master

Update to latest barcode scanner