Update squid3 to 3.5.2 (Squid 3.5.3).

Changes to squid-3.5.2 (18 Feb 2015):

- Regression Bug 4176: Digest auth too many helper lookups
- Regression Bug 4180: not-fully-initialized data member in ACLUserData
- Bug 4172: Solaris broken krb5-config
- Bug 4073: Cygwin compile errors
- Bug 3919: remove several never-true / never-false comparisons
- HTTPS: Add missing root CAs when validating chains that passed internal checks
- Fix some cbdataFree related memory leaks
- Quieten CBDATA 'leak' messages
- Set SNI information in transparent bumping mode
- negotiate_kerberos_auth: fix krb5.conf backward compatibility
- Fix memory leaks in cachemgr.cgi URL parser
- Fix sslproxy_options in peek-and-splice mode
- ... and fix several portability and build issues
- ... and some documentation updates
- ... and all fixes from squid 3.4.11

(taca)