[v3] more istream::ignore cleanups

[Paolo Carlini]

Gabriel Dos Reis wrote:

>Paolo Carlini <pcarlini@suse.de> writes:
>
>| The problem is, on 32-bit machines, LFS enabled, your file can be
>| bigger that 2G, thus more than 2G chars to ignore, in general, whereas
>| streamsize, being basically a ptrdiff_t, is still limited to 32-bit:
>| we are at risk of *signed* integer overflow, which is absolutely
>| verboten!!! Still, we want to allow the user to keep on using ignore,
>| in the general, unlimited form, also on such platforms...
>
>I think it is written somewhere in the rules that max() morally
>corresponds to unbounded ignore, unless the stream is corrupted or EOF
>is reached.
>  
>
Indeed, this is *exactly* what I meant.

>| If you want, I can add comments...
>
>That would be most welcome.  Thanks!
>  
>
Right. Will do together with fixing a very subtle corner-case which predates
my recent changes.

Paolo.