display filename in advanced mode

Hi, I found annotating filename very helpful for as below, I had a very small patch to do this, I am not sure closure developers find this interesting(it maybe not that precise, but it is good enough for me to guess which code does it come from), if so, I am more than happy to submit a small patch

``` js
// Input 0./caml_exceptions.js
'use strict';
// Input 1./caml_array.js
// Input 2./caml_utils.js
// Input 3./caml_string.js
// Input 4./caml_primitive.js
var a = 0;
// Input 5./caml_format.js
// Input 6./caml_io.js
// Input 7./camlinternalFormatBasics.js
// Input 8./pervasives.js
a++;
// Input 9./list.js
// Input 10./char.js
// Input 11./bytes.js
// Input 12./string.js
// Input 13./sys.js
a++;
// Input 14./caml_float.js
// Input 15./buffer.js
// Input 16./camlinternalFormat.js
a++;
// Input 17./printf.js
// Input 18./arg.js
a++;
a++;
a++;

```