mono/mono — pull request #914 by eiz (2014-02-25 09:10:27+00:00)
Title: Fix memory leak.

Introduced in b322a6e41038f7bf35f8a433b34c3b18e4a6d169. variance_used
was not being set before use, resulting in leaked trampolines when
calling methods on variant interfaces.

Test case:
```csharp
using System;
using System.Collections;
using System.Collections.Generic;

public interface I {
T Current { get; }
}

public struct X: I {
public T Current { get { return default(T); } }
}

public class TestCase {
static object Dummy;

private void BusyWork(I