[mod_auth] http_auth_const_time_memeq improvement
[mod_auth] http_auth_const_time_memeq improvement

employ volatile, which might matter with some compilers (or might not)
explicitly check that string lengths match
  (or else might match string where last char of short string matches
   repeated chars in longer string)

gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4