"range" header is copied from container options even though it should be transitory

[davedx]

In lib/requestOptions.js, we do this:

var hds = extend(headers, req.headers, skipHdrs);

But this will also copy the "range" header from the headers variable (which comes from Container.options), even if the client has not set any range header. The result is any requests /after/ a request that used the 'range' header to break up a response will break, often with 416 errors from the origin server, because the range header is still set from a previous resource.