[Patch] Fix libstdc++/7744

[Benjamin Kosnik]

Paolo, this looks good modulo small bits below.

>P.S. Benjamin, in my private message I forgot _your_ 9780!

Not quite sure what you mean here. Can you help me out?

-benjamin

+  // block until the asked number of bytes is available.

should be

+  // block until the asked number of bytes are available.


 	      pos_type __tmp =
-		_M_file.seekoff(__off, ios_base::cur, __mode);
+		_M_file.seekoff(__off, ios_base::cur, __sync, __mode);


should be

 	      pos_type __tmp = _M_file.seekoff(__off, ios_base::cur, 
                                               __sync, __mode);