Medium Trust: Update Weak class to not extend WeakReference and avoid demaning inheritancedemand security permission.

--HG--
branch : dev

src/Orchard/Caching/Weak.cs

@@ -1,23 +1,20 @@
 using System;
-using System.Runtime.Serialization;
 
 namespace Orchard.Caching {
-    public class Weak<T> : WeakReference {
-        public Weak(T target)
-            : base(target) {
+    public class Weak<T> {
+        private readonly WeakReference _target;
+
+        public Weak(T target) {
+            _target = new WeakReference(target);
         }
 
-        public Weak(T target, bool trackResurrection)
-            : base(target, trackResurrection) {
+        public Weak(T target, bool trackResurrection) {
+            _target = new WeakReference(target, trackResurrection);
         }
 
-        protected Weak(SerializationInfo info, StreamingContext context)
-            : base(info, context) {
-        }
-
-        public new T Target {
-            get { return (T)base.Target; }
-            set { base.Target = value; }
+        public T Target {
+            get { return (T)_target.Target; }
+            set { _target.Target = value; }
         }
     }
 }