CLANG 3.2 breaks security/pam_ssh_agent_auth on stable/9

[James]

I was able to correct the problem as well by prefixing strnvis, avoiding
the symbol collision. I also found PR: ports/172941 which also has a fix.

Using my patch or the patch in ports/172941 fixes the segfault for me in
stable/9. However, I quickly ran into another problem. I can't remember the
error message exactly, it was something like "Unable to initialize PAM:
Unknown file descriptor". A ktrace didn't reveal anything obvious. I'll try
to test it out tomorrow.

-- 
James.