Fixed wrongly casting Exceptions to WorkItem's TResult

Also added UnitTest

Thanks to Zdenek who pointed this.

STPTests/TestExceptions.cs

@@ -77,11 +77,29 @@ namespace SmartThreadPoolTests
 			Assert.IsTrue(e is DivideByZeroException);
 		}
 
-		private object DoDiv(object state)
+        private object DoDiv(object state)
-		{ 
+        {
-			DivArgs divArgs = (DivArgs)state;
+            DivArgs divArgs = (DivArgs)state;
-			return (divArgs.x / divArgs.y);
+            return (divArgs.x / divArgs.y);
-		}
+        }
 
+        [Test]
+		public void ExceptionType()
+		{ 
+			SmartThreadPool smartThreadPool = new SmartThreadPool();
+
+	        var workItemResult = smartThreadPool.QueueWorkItem(new Func<int>(ExceptionMethod));
+
+            smartThreadPool.WaitForIdle();
+
+            Assert.IsInstanceOf<NotImplementedException>(workItemResult.Exception);
+
+            smartThreadPool.Shutdown();
+        }
+
+	    public int ExceptionMethod()
+        {
+            throw new NotImplementedException();
+        }
 	}
 }

SmartThreadPool/WorkItemResultTWrapper.cs

@@ -103,7 +103,7 @@ namespace Amib.Threading.Internal
 
         public object Exception
         {
-            get { return (TResult)_workItemResult.Exception; }
+            get { return _workItemResult.Exception; }
         }
 
         #region IInternalWorkItemResult Members