Warn when object.Equals is used for comparing structs

[SergeyTeplyakov]

It seems that it can't be correct since boxing will create a new instance every time.

[SergeyTeplyakov]

The behavior is correct, but we'll box the arguments.

[SergeyTeplyakov]

object.ReferenceEquals for structs is meaningless.

[SergeyTeplyakov]

But for object.ReferenceEquals there is an existing fxcop rule.