NetBSD the thread safe resolver is only available on __NetBSD_Version__
>= 299000900. Fixes runtime usage on NetBSD 2.1. New Versions:
- firefox-1.0.6nb2
- firefox-gtk1-1.0.6nb2
- mozilla-1.7.11nb1
- mozilla-gtk2-1.7.11nb1
- thunderbird-1.0.6nb1
- thunderbird-gtk1-1.0.6nb1