[Network] silently quits upon selecting DNS settings

[diver]

hrev49371.

Clicking DNS settings in Network preflet quits with _res is not supported for multi-threaded programs. message.

[jua]

The DNS network settings use the global __res API which, according to [0], has been out of favour for a long time. In hrev49371 I switched our netresolv to use the thread-safe version of the res functions, which are also used internally by getaddrinfo() and others (for further explanation see the commit message). It was necessary because the thread-unsafe version broke name resolution in the Services Kit (as soon as more than one request happened at the same time).

However, the thread-safe implementation doesn't support the old __res_state() API at all anymore, hence this bug. On the NetBSD problem report in [0] it is recommended to use a local _res_state via res_ninit() and res_nclose() instead. I'm not familiar with these APIs - maybe Axel can comment if that would be feasible?

Other options would be extending netresolv ourselves to allow using this (basically, providing a mix of NetBSD's thread-safe and thread-unsafe functions, not a good choice I think), or switching to a different implementation altogether.

[0] ​http://gnats.netbsd.org/46661 (thanks to Diver for providing the link)