The attached patch adds various tests for res_init and other 
initialization functions.  Bugs 21474 (already fixed) and 21475 were 
discovered while writing these tests.  I did not bother to fix bug 21475 
(search path truncation) because it will be gone with a larger 
resolv.conf parser rewrite anyway.

The tests use various namespace kludges to be able to test unmodified 
binaries, which have a hardcoded /etc/resolv.conf path.  On current 
Fedora, no root privileges are required, which is why didn't make this 
an xtest.

The patch as written depends on the subprocess capture functionality in 
the dynarray patch

   https://sourceware.org/ml/libc-alpha/2017-04/msg00498.html

but I could cherry-pick the support functionality from there before 
committing (or use a different mechanism to capture the deserialized 
resolv.conf data, such as the new shared memory allocator).

Comments?

Thanks,
Florian