[PATCH] Fix libstdc++/5708

[Paolo Carlini]

Nathan Myers wrote:

> I don't agree that we have license to assume "space" may be replaced with
> __fill in the output format.   The subject has not (to my knowledge) been
> reported as a Defect to the committee.  This change strikes me as a source
> of interoperability problems, as sensible as it might seem otherwise.

Another thing: as Peter Schmid noticed, Nico Josuttis believes too that "Where a
space character has to appear, the character /fill/ is inserted".

Ciao, Paolo.