KNOWN_BUGS: 1.8 DNS timing is wrong for HTTP redirects

Closes #522

docs/KNOWN_BUGS

@@ -19,6 +19,7 @@ problems may have been fixed or changed somewhat since this was written!
  1.5 Expect-100 meets 417
  1.6 Unnecessary close when 401 received waiting for 100
  1.7 CONNECT response larger than 16KB
+ 1.8 DNS timing is wrong for HTTP redirects
 
  2. TLS
  2.1 Hangs with PolarSSL
@@ -126,6 +127,12 @@ problems may have been fixed or changed somewhat since this was written!
  will return prematurely and will confuse the rest of the HTTP protocol
  code. This should be very rare.
 
+1.8 DNS timing is wrong for HTTP redirects
+
+ When extracting timing information after HTTP redirects, only the last
+ transfer's results are returned and not the totals:
+ https://github.com/curl/curl/issues/522
+
 
 2. TLS