Failing test for Html.CheckBoxFor() - cannot submit bool=true

Html.CheckBoxFor creates a second hidden input for the bool to ensure that
the false value is set with the post. But in the case of a true value,
both the checkbox and hidden input values are sent with the form.
ServiceStack sees this data as a list and has trouble deserializing the
list into a bool.

StackTrack:
```
ERROR|EndpointHandlerBase|Error occured while Processing Request: Unable to bind request|ServiceStack.WebHost.Endpoints.RequestBindingException: Unable to bind request ---> System.Runtime.Serialization.SerializationException: KeyValueDataContractDeserializer: Error converting to type: String was not recognized as a valid Boolean. ---> System.FormatException: String was not recognized as a valid Boolean.
   at System.Boolean.Parse(String value)
   at ServiceStack.Text.Common.DeserializeBuiltin`1.<GetParseFn>b__0(String value)
   at ServiceStack.Text.Common.JsReader`1.<>c__DisplayClassb`1.<GetCoreParseFn>b__7(String value)
   at ServiceStack.ServiceModel.Serialization.StringMapTypeDeserializer.PopulateFromMap(Object instance, IDictionary`2 keyValuePairs, List`1 ignoredWarningsOnPropertyNames) in c:\code\github\ServiceStack\src\ServiceStack.Common\ServiceModel\Serialization\StringMapTypeDeserializer.cs:line 108
   --- End of inner exception stack trace ---
   at ServiceStack.ServiceModel.Serialization.StringMapTypeDeserializer.PopulateFromMap(Object instance, IDictionary`2 keyValuePairs, List`1 ignoredWarningsOnPropertyNames) in c:\code\github\ServiceStack\src\ServiceStack.Common\ServiceModel\Serialization\StringMapTypeDeserializer.cs:line 132
   at ServiceStack.ServiceHost.RestPath.CreateRequest(String pathInfo, Dictionary`2 queryStringAndFormData, Object fromInstance) in c:\code\github\ServiceStack\src\ServiceStack\ServiceHost\RestPath.cs:line 351
   at ServiceStack.WebHost.Endpoints.RestHandler.GetRequest(IHttpRequest httpReq, IRestPath restPath) in c:\code\github\ServiceStack\src\ServiceStack\WebHost.Endpoints\RestHandler.cs:line 107
   --- End of inner exception stack trace ---
   at ServiceStack.WebHost.Endpoints.RestHandler.GetRequest(IHttpRequest httpReq, IRestPath restPath) in c:\code\github\ServiceStack\src\ServiceStack\WebHost.Endpoints\RestHandler.cs:line 111
   at ServiceStack.WebHost.Endpoints.RestHandler.ProcessRequest(IHttpRequest httpReq, IHttpResponse httpRes, String operationName) in c:\code\github\ServiceStack\src\ServiceStack\WebHost.Endpoints\RestHandler.cs:line 62
```