Update to squid 4.0.21.

Also use bash traps to signal shutdown to squid.

docker-squid/Dockerfile

@@ -4,7 +4,7 @@ RUN sed s:deb:deb-src: /etc/apt/sources.list >> /etc/apt/sources.list
 
 RUN apt-get update && apt-get build-dep -y squid3 && apt-get install -y wget tar xz-utils libssl-dev
 
-ARG SQUID_VERSION=4.0.13
+ARG SQUID_VERSION=4.0.21
 
 # TODO: verify the squid download with the signing key
 RUN mkdir /src \

docker-squid/squid.bsh

@@ -106,8 +106,16 @@ if [ "$PROXYCHAIN" = "yes" ]; then
         exit 1
     fi 
     # Start squid with proxychains
-    exec proxychains4 squid -N
+    proxychains4 squid -N &
+    PID=$!
 else
     # Start squid normally
-    exec squid -N
+    squid -N &
+    PID=$!
 fi
+
+# This construct allows signals to kill the container successfully.
+trap "kill -TERM $PID" INT TERM
+wait $PID
+wait $PID
+exit $?