[Patch, RFC] Remove bogus fflush

[Benjamin Kosnik]

>Now, turns out that the library still has some, essentially bogus, we
>believe, fflush, remnants of the old __basic_file<> implementation,
>used in 3.3, which exploited the stdio API (i.e., fread, fwrite,
>fflush, and so on).
>
>Indeed, the below regtests OK on x86 and x86_64 linux.

Sorry Paolo, I'm just getting to this.

Did you test with the interactive tests? I would suggest a run through
those just to be safe. Since they are not part of the normal test runs,
maybe something will show up.

best,
benjamin