Invoke specialized write for <response>

[kibook]

The <response> type has a specialized version of write and write-element defined in server/core/response.dylan for <response> and <byte-string>, but copy-to-end here instead called a more generic version for <stream> and <sequence>.

This meant the <response> was being written to as a normal stream, instead of using the maybe-send-chunk method and writing to response.response-stream.

Coercing the parameters to the types expected by the write and write-element methods in server/core/response.dylan fixes an issue with <directory-resource> serving static files.

[cgay]

The write method called should be determined by the run-time types of both arguments. stream must already be a <response>, otherwise as(<response>, stream) would err. I surmise that buffer is not a <byte-string> and that's why it was failing to call write(<response>, <byte-string>). Could you verify that?

Rather than copy the buffer with as(<byte-string>, buffer) I think it would be better to define a write(<response>, <sequence>) method next to the write(<response>, <byte-string>) method. (Keep the original method so that byte strings remain relatively fast.)

[cgay]

It's a good idea to have a more general method there because this is an easy mistake to make and it's better to work and be slow than to pretend to work.

[kibook]

Yes, the buffer used in copy-to-end was just <sequence>, which was why the write method in server/core/response.dylan wasn't being called.

[cgay]

kibook, it would be good if you could remove the reverted change from this pull request before we merge it. Otherwise it looks good. Thanks!