external_acl_type requests authentication

http://www.squid-cache.org/mail-archive/squid-users/200801/0364.html

Okay, this version might even work. Once I realised i had to reimplement the
original patch it was easy. There I go, tempting fate again.

http://www.squid-cache.org/bugs/show_bug.cgi?id=1278

Caveats. I don't know all the code (there's 70k lines, it might take a while).
The new struct member name and the function name suck, but match what's
already there.

-- 
ian j hart