Allow to set Expires attribute

to a date in theast. See #479

codec-http/src/main/java/io/netty/handler/codec/http/Cookie.java

@@ -87,7 +87,7 @@ public interface Cookie extends Comparable<Cookie> {
     void setComment(String comment);
 
     /**
-     * Returns the maximum age of this {@link Cookie} in seconds.
+     * Returns the maximum age of this {@link Cookie} in seconds or {@link Long#MIN_VALUE} if unspecified
      *
      * @return The maximum age of this {@link Cookie}
      */
@@ -97,7 +97,7 @@ public interface Cookie extends Comparable<Cookie> {
      * Sets the maximum age of this {@link Cookie} in seconds.
      * If an age of {@code 0} is specified, this {@link Cookie} will be
      * automatically removed by browser because it will expire immediately.
-     * If {@code -1} is specified, this {@link Cookie} will be removed when the
+     * If {@link Long#MIN_VALUE} is specified, this {@link Cookie} will be removed when the
      * browser is closed.
      *
      * @param maxAge The maximum age of this {@link Cookie} in seconds

codec-http/src/main/java/io/netty/handler/codec/http/DefaultCookie.java

@@ -35,7 +35,7 @@ public class DefaultCookie implements Cookie {
     private boolean discard;
     private Set<Integer> ports = Collections.emptySet();
     private Set<Integer> unmodifiablePorts = ports;
-    private long maxAge = -1;
+    private long maxAge = Long.MIN_VALUE;
     private int version;
     private boolean secure;
     private boolean httpOnly;

codec-http/src/main/java/io/netty/handler/codec/http/ServerCookieEncoder.java

@@ -54,7 +54,7 @@ public final class ServerCookieEncoder {
 
         add(buf, cookie.getName(), cookie.getValue());
 
-        if (cookie.getMaxAge() >= 0) {
+        if (cookie.getMaxAge() != Long.MIN_VALUE) {
             if (cookie.getVersion() == 0) {
                 addUnquoted(buf, CookieHeaderNames.EXPIRES,
                         new HttpHeaderDateFormat().format(