[Libpqxx-general] Support char & unsigned char types

[Jeroen Vermeulen]

Maxime van Noppen wrote:

> I found at least a bug with this patch (not so straightforward it seems
> :)). I was (too) lazy and just casted the (unsigned) char into an
> (unsigned) int to reuse the to_string_(un)signed functions but this
> doesn't produce the expected output.

Whether char is signed or unsigned is implementation-defined, i.e. the 
compiler can decide.  We can't make assumptions about that.


Jeroen