Eliminate redundancy of dup/idup

[Steven Schveighoffer]

On Sun, 09 Sep 2012 11:32:10 -0400, kenji hara <k.hara.pg at gmail.com> wrote:

> I've posted two pull requests for the purpose.
>
> https://github.com/D-Programming-Language/dmd/pull/1110
> https://github.com/D-Programming-Language/druntime/pull/298
>
> inout parameter and strongly purity function can realize this.
>

Excellent!  I have been waiting for this for a long time.

-Steve