Mono 3.1.2 发布了，这是一个Bug修正版本，修复了如下 bug：
10782 - Emit additional sequence points for call entry when needed.
12989 - Loading of nested type of missing type needs to create another missing type.
13110 - Equality structural comparer needs to do recursive comparisons.
13197 - Allow async for explicitly implemented interface methods.
13200 - Implement webrequest cancellation.
13202 - Prefer user operators over predefined operators for binary enum operations too.