issue1201: Tracing extension methods should interpret HttpResponseException
    - move `TranslateHttpResponseException` from `SystemDiagnosticsTraceWriter`
      to `TraceWriterExceptionMapper.cs`.
    - Both assemblies of System.Web.Http and System.Web.Http.Tracing link to
      `TraceWriterExceptionMapper.cs`, `TraceWriterExceptionMapperResources.resx`,
      and `TraceWriterExceptionMapper.Designer.cs`.
    - modify `catch` block for HttpResponseExceptions in TraceBeginEnd* methods.
    - add unit tests for each mehtod.