c# 'Name' is a namespace but is used like a type

Issue description

Starting post 2.3.1, at least 2.4.1, C#.NET code can throw the above compile error where the namespace is the same as a type. This is reasonable, but in earlier versions, the generator added "Model" to the type, eg "ModelEvent" instead of "Event" (where a namespace "Event and type Event co-exist in the definition).

Swagger-codegen version

2.4.1 and above including latest version 3.0.20.

Swagger declaration file content or url

Not easy to post a definition file as it's proprietary to another company. But the issue is fairy generic to where a namespace and type definition have the name.

Command line used for generation

java -jar swagger-codegen-cli-2.4.1.jar generate -i "Event.swagger.json" -l csharp -o "Event" -c "Event.config.json"

Steps to reproduce

The config file looks like:

"packageName": "SKYLib.Event",
"targetFramework": "v4.5",
"modelPropertyNaming": "PascalCase",
"nonPublicApi": "false",
"sortParamsByRequiredFlag": "true",
"useCollection": "false",
"validatable": "false",
"optionalAssemblyInfo": "false",
"optionalEmitDefaultValues": "false",
"optionalMethodArgument": "true",
"optionalProjectFile": "false"

Related issues/PRs

I've search and tried to locate the change between 2.3.1 and 2.4.1 but there isn't enough detail to be sure of the source.

Suggest a fix/enhancement

I know I can add a model prefix during generation using a generate argument, but this is less attractive than what I assume was conflict detection in previous versions.

Start by reproducing the generated C# output with Event.swagger.json, Event.config.json, and the shown swagger-codegen command, comparing versions 2.3.1 and 2.4.1. Trace how the csharp generator handles a namespace and model with the same name; done means generation no longer produces the compile error without requiring a model prefix.