Fix netdb.h addrinfo namespace (bug 18529)

[Joseph Myers]

On Fri, 12 Jun 2015, Roland McGrath wrote:

> Again fine but I think the public header should get a comment.

I've made the existing comment refer to POSIX.1:2001 instead of POSIX.1g 
(a reference to POSIX.1:2001 seems the most useful in terms of the 
standards supported by glibc).  I don't think the fact that there was once 
a bug is particularly useful information to go in comments in the header.

> I also think all these user-visible API changes merit NEWS items
> (perhaps several of them could be covered by a single item).

I think of these changes (that do not affect _DEFAULT_SOURCE or 
_GNU_SOURCE and do not obsolete or remove any API) as much like any other 
ordinary bug fix - that is, something for which the entry in the list of 
fixed bugs is sufficient.  If, on review of the changes since 2.21 during 
the freeze for 2.22, it seems these API bug fixes are a significant enough 
group of changes to be worth calling out, they could always be mentioned 
in a general item (but without trying to list details of each individual 
bug that was fixed).

-- 
Joseph S. Myers
joseph@codesourcery.com