Support for %d$c format specifier

[Bruce Korb]

> My plan is 
>  - (1) first to incorporate the C++, and C extension into the positional 
>        paramter handling framework by extending the
>        protocol between the decoder and diagnostic.c.
> 
>        This is necesary for the positional parameter handling to
>        be usable.

I confess I don't read everything on gcc/gcc-patches, so perhaps
I missed something.  Is there a reason not to use a pre-existing
library for this stuff?  e.g.:

  http://savannah.nongnu.org/projects/libsnprintfv/

especially given:

> However, we have a limited man-power obvioulsy.