Bug#790065: Make output of texinfo index deterministic

[Patrice Dumas <pertusus@free.fr>]

On Mon, Jun 29, 2015 at 07:36:26AM +0900, Norbert Preining wrote:
> Dear all,
> 
> This appears to happen because the index sort is not stable with respect
> to the line number, resulting in output non-determinstically changing
> from:                                                                           
> The attached patch adds the line number to the sort comparator. Once
> applied, (some) packages using texinfo can be built reproducibly in
> our reproducible toolchain.

I committed a fix.

I used the @-command name to disambiguate, as it should always be
different otherwise the entries are in the same index and number is
enough to have a reproducible sorting.

-- 
Pat