Fix NET35 build

NET35 doesn't seem to support Expression.Variable.

Added back previous DelegateProxyFactory implementation from
ac140ef7ba for NET35 target only.

Updated test accordingingly.

Source/NSubstitute.Acceptance.Specs/FieldReports/Issue271_DelegateOutArgument.cs

@@ -15,7 +15,11 @@ namespace NSubstitute.Acceptance.Specs.FieldReports
 
             foo(out bar);
 
+#if NET4 || NET45
             Assert.AreEqual(42, bar);
+#else
+            Assert.Ignore("Not supported for NET35");
+#endif
         }
     }
 }

Source/NSubstitute/Proxies/DelegateProxy/DelegateProxyFactory.cs

@@ -41,6 +41,28 @@ namespace NSubstitute.Proxies.DelegateProxy
             ParameterExpression[] proxyParameters = delegateMethodToProxy.GetParameters().Select(x => Expression.Parameter(x.ParameterType, x.Name)).ToArray();
             Expression[] proxyParametersAsObjects = proxyParameters.Select(x => (Expression)Expression.Convert(x, typeof(object))).ToArray();
 
+#if NET35
+            Expression callInvokeOnDelegateCallInstance =
+                Expression.Call(
+                    Expression.Constant(delegateCall),
+                    invokeOnDelegateCall,
+                    new Expression[]
+                    {
+                        Expression.NewArrayInit(typeof(object), proxyParametersAsObjects)
+                    }
+                );
+
+            if (delegateMethodToProxy.ReturnType != typeof(void))
+            {
+                callInvokeOnDelegateCallInstance =
+                    Expression.Convert(callInvokeOnDelegateCallInstance, delegateMethodToProxy.ReturnType);
+            }
+
+            var proxyExpression = Expression.Lambda(delegateType, callInvokeOnDelegateCallInstance, proxyParameters);
+            return proxyExpression.Compile();
+#endif
+#if !NET35
+
             var bodyExpressions = new List<Expression>();
             bool isVoid = delegateMethodToProxy.ReturnType == typeof(void);
             var arguments = Expression.Variable(typeof(object[]), "arguments");
@@ -71,6 +93,7 @@ namespace NSubstitute.Proxies.DelegateProxy
             var variables = isVoid ? new[] { arguments } : new[] { arguments, result };
             var proxyExpression = Expression.Lambda(delegateType, Expression.Block(variables, bodyExpressions), proxyParameters);
             return proxyExpression.Compile();
+#endif
         }
     }
 }