squid: Update to 3.5.19

squid: Update to 3.5.19

Activated 'ipv6', as discussed in ipfire-list with Michael:

"I had a look what the IPv6 switch actually changes. And that is not really much.
Essentially nothing. It just probes if the system supports IPv6 and if not it
disables it internally.

http://git.ipfire.org/?p=thirdparty%2Fsquid.git&a=search&h=refs%2Fheads%2Ftrunk&st=grep&s=USE_IPV6

I think we can as well enable this."

Signed-off-by: Matthias Fischer <matthias.fischer@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>