Do not un-escape forward slashes in the request path

[Tratcher]

WebListener sits on Http.Sys and consumes it's CookedUri by default. Http.Sys defensively un-escapes %2F to a forward slash in violation of the spec. This breaks OData and other frameworks. HttpListener had an app.config setting (https://msdn.microsoft.com/en-us/library/ee624078%28v=vs.110%29.aspx?f=255&MSPPError=-2147217396) where you could ask it to re-parse the path without un-escaping %2F. WebListener should have this behavior by default.

For aspnet/KestrelHttpServer#124 we need something similar, so let's put this in shared code.

[muratg]

cc @troydai

[Tratcher]

Most of the code already exists in https://github.com/aspnet/WebListener/blob/dev/src/Microsoft.Net.Http.Server/RequestProcessing/RequestUriBuilder.cs#L70-L71, we just need to turn it on and validate it.