build fix for VS2010: IVsDifferenceCodeWindow doesn't exist in VS2010
build fix for VS2010: IVsDifferenceCodeWindow doesn't exist in VS2010

Microsoft/PTVS,DEVSENSE/PTVS,Microsoft/PTVS,huguesv/PTVS,int19h/PTVS,int19h/PTVS,DEVSENSE/PTVS,huguesv/PTVS,DEVSENSE/PTVS,Microsoft/PTVS,zooba/PTVS,Microsoft/PTVS,int19h/PTVS,int19h/PTVS,Microsoft/PTVS,zooba/PTVS,DEVSENSE/PTVS,huguesv/PTVS,DEVSENSE/PTVS,zooba/PTVS,zooba/PTVS,zooba/PTVS,zooba/PTVS,DEVSENSE/PTVS,huguesv/PTVS,huguesv/PTVS,Microsoft/PTVS,int19h/PTVS,int19h/PTVS,huguesv/PTVS