Implementation of C11 Bounds-checking interfaces

[Ulrich Bayer]

> 
> Some more notes on behavior/conformance:
> 
> freopen_s: It is not conformant to call fclose and then fopen_s.
> freopen is required to return the argument passed to it on success,
> not a new FILE pointer. I think wrapping freopen would work just fine
> and would also handle the case where the filename argument is NULL.
> 
> gets_s: Very slow and does not perform the necessary locking to make
> the whole operation atomic. You should just call fgets and then remove
> the trailing newline if gets_s is supposed to behave like gets and do
> that.
> 
> Rich

Thanks! I will look at this and try to change the implementation
accordingly.

Ulrich