[Patch] Reimplement (and split) istream::ignore

[Benjamin Kosnik]

This looks fine Paolo with this one bit:

>+        *  NB: Conformingly, we provide three overloads, instead of the single
>+        *  function (with defaults) mandated by the Standard: this leads to a
>+        *  better performing implementation.

Should be: 

>+        *  NB: Provide three overloads, instead of the single
>+        *  function (with defaults) mandated by the Standard: this leads to a
>+        *  better performing implementation, while still conforming to the standard.

You might also want to detail, in an abbreviated summary, why it's a
"better performing implementation."

best,
benjamin