squid: Update to 3.5.18

squid: Update to 3.5.18

Removed unecessary quotations and two configure-options, see:
ftp://ftp.fu-berlin.de/unix/www/squid/archive/3.1/squid-3.1.0.16-RELEASENOTES.html

--with-aio
Deprecated. POSIX AIO is now auto-detected and enabled.
Use --without-aio to disable, but only if you really have to.

--with-pthreads
Deprecated. pthreads library is now auto-detected and enabled.
Use --without-pthreads to disable, but only if you really have to.

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