Bump to squid 3.4.6 and use pf instead of ipfw

I tried, `ENV.append "CPPFLAGS", "-Wno-error=deprecated-declarations"` can be dropped.
Without `ENV.append "LDFLAGS",  "-lresolv"`, there are link errors:
```
libtool: link: clang++ -Werror -Qunused-arguments -D_REENTRANT -g -O2 -march=native -g -o ext_kerberos_ldap_group_acl kerberos_ldap_group.o support_group.o support_netbios.o support_member.o support_krb5.o support_ldap.o support_sasl.o support_resolv.o support_lserver.o support_log.o -dynamic -Wl,-search_paths_first -dynamic -Wl,-search_paths_first -Wl,-bind_at_load  ../../../lib/.libs/libmiscencoding.a ../../../compat/.libs/libcompat-squid.a -lldap -llber -lsasl2 -lkrb5
Undefined symbols for architecture x86_64:
  "_res_9_dn_expand", referenced from:
      get_ldap_hostname_list(main_args*, hstruct**, unsigned long, char*) in support_resolv.o
  "_res_9_search", referenced from:
      get_ldap_hostname_list(main_args*, hstruct**, unsigned long, char*) in support_resolv.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
```

Possible related upstream ticket is http://bugs.squid-cache.org/show_bug.cgi?id=4023