Log Message:
Update squid to 3.5.21.

Changes to squid-3.5.21 (08 Sep 2016):

	- Bug 4563: duplicate code in httpMakeVaryMark
	- Bug 4542: authentication credentials IP TTL updated incorrectly
	- Bug 4534: assertion failure in xcalloc when using many cache_dir
	- Bug 4428: mal-formed Cache-Control:stale-if-error header
	- Bug 3025: Proxy-Authenticate problem using ICAP server
	- Fix segfault via Ftp::Client::readControlReply()
	- Fix SSL-Bump failure results in SEGFAULT
	- HTTP/1.1: MUST always revalidate Cache-Control:no-cache responses
	- HTTP/1.1: do not allow Proxy-Connection to override Connection header
	- SSL: CN wildcard must only match a single domain component [fragment]