Made AbstractLicenseValidator implement IDisposable

Not sure what "fancy-word"-principle this seems to break but essentially
every time you instantiate the AbstractLicenseValidator it would create
a timer thread which would never be removed until the garbage collector
did its job. This is a very strange behavior because it forces us to
call DisableFutureChecks as if it was a dispose method. This opens up
the license validator to be used in bigger server environments.

Rhino.Licensing/AbstractLicenseValidator.cs

@@ -15,7 +15,7 @@ namespace Rhino.Licensing
     /// <summary>
     /// Base license validator.
     /// </summary>
-    public abstract class AbstractLicenseValidator
+    public abstract class AbstractLicenseValidator : IDisposable
     {
         /// <summary>
         /// License validator logger
@@ -41,6 +41,7 @@ public abstract class AbstractLicenseValidator
             "nist1.sjc.certifiedtime.com"
         };
 
+        private bool disposed;
         private readonly string licenseServerUrl;
         private readonly Guid clientId;
         private readonly string publicKey;
@@ -563,5 +564,32 @@ public void DisableFutureChecks()
             disableFutureChecks = true;
             nextLeaseTimer.Dispose();
         }
+
+        public void Dispose()
+        {
+            Dispose(true);
+            GC.SuppressFinalize(this);
+        }
+
+        ~AbstractLicenseValidator()
+        {
+            Dispose(false);
+        }
+
+        protected virtual void Dispose(bool disposing)
+        {
+            if (disposed)
+                return;
+
+            if (disposing)
+            {
+                nextLeaseTimer.Dispose();
+            }
+
+            // release any unmanaged objects
+            // set the object references to null
+
+            disposed = true;
+        }
     }
 }