[PATCH] Update backward/algo.h

[Paolo Carlini]

Gabriel Dos Reis wrote:

> | It may be necessary to give ext/algorithm a suffix, or to make it
> | sub-include ext/bits/algorithm.h, and make algo.h include that
> | directly.
>
> I don't think that is necessary.  Did you have a look at the rest of
> files in ext/?  Those have been there for longtime.

Gaby, Nathan, do you think I can commit, at least for the moment, my very short
patch for backward/algo.h? In this way that header file is fully functional
again.

Thanks,
Paolo.