There's Squid 3.1.18 available: http://www.squid-cache.org/Versions/v3/3.1/changesets/SQUID_3_1_17.html http://www.squid-cache.org/Versions/v3/3.1/changesets/SQUID_3_1_18.html
Good news! It seems that bumping 3.1.16 to .18 works out of the box; no patches necessary for a change.
+ 24 Dec 2011; Patrick Lauer <patrick@gentoo.org> +squid-3.1.18.ebuild: + Bump for #395195