0-length basic_istream::read() fails

[Benjamin Kosnik]

> Following some of the recent changes to istream, some of my code broke.
> I tracked it down to the fact that basic_istream::read is now setting
> failbit if the length argument __n is zero.  (It also looks like
> it consumes a character in that case, which is lost.)

Fair enough. I changed your patch slightly, and made readsome consistent 
with read. I believe the new, changed behavior is conformant to the 
standard. . . actually, I think istream in general, is conforming now.

It's in, thanks. 

-benjamin