Merge NRefactory changes from SharpDevelop to NRefactory repository.

* Fix NRE in TypeGuessing after `yield return new`
* Add message text to CS0618UsageOfObsoleteMemberIssue
* Fix IndexOutOfRangeException in AddOptionalParameterToInvocationAction
* Fix icsharpcode/SharpDevelop#580: EventHandler names suggested by code completion should include the variable name/expression.
* Fix icsharpcode/SharpDevelop#574: Wrong error highlighting with interface implementation