rdmd with a file with no extension

[Colin via Digitalmars-d-learn]

When running a small D program through rdmd, it seems the file 
needs a .d extension to work.

```
$ ./testscript2
Error: module testscript2 is in file './testscript2.d' which 
cannot be read

$ cat testscript2
#!/usr/bin/env rdmd

void main(string[] args){
    import std.stdio;

    writeln(args);
}

```

Trying the above on OSX if that makes a difference.

Any way to get these to work short of renaming it testscript2.d?