squid: Update to 4.6

For details see:
http://www.squid-cache.org/Versions/v4/changesets/

The 'configure'-option "--disable-ipv6" was removed, it is no longer necessary.

See:
https://lists.ipfire.org/pipermail/development/2016-April/002046.html

"The --disable-ipv6 build option is now deprecated.
...
Squid-3.5.7 and later will perform IPv6 availability tests on startup in
all builds.

- Where IPv6 is unavailable Squid will continue exactly as it would
have had the build option not been used.

These Squid can have the build option removed now."

The warning message concerning a "BCP 177 violation" while
starting 'squid' can be ignored.

Best,
Matthias

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