Array does not work

The following does not compile (`attributes::sourceCpp(test.cpp)`, see also comment on #156):

``` cpp
#include <Rcpp.h>
using namespace Rcpp ;

typedef Array<3,REALSXP> Numeric3D ;

// [[Rcpp::export]]
Numeric3D test(){
  Numeric3D res(1,1,1);
  return res;
}

/*** R
test()
*/
```
