Change drupal_http_reqeust to use HTTP 1.1

Issue Summary

Hi folks,

I've been playing with using gzip compression between a web service using nginx and drupal. Drupal's http_client is nice and lightweight, but it lacks some options which more full fledged ones have (Like pear's HTTP_Request).

One of them is the HTTP version to use. I suggest either changing this to 1.1 in the code, or providing it as an option.

My current discovery is that nginx out of the box, does not support gzip_encoding on 1.0 spec, and here is why:

When HTTP version 1.0 is used, the Vary: Accept-Encoding header is not set. As this can lead to proxy cache corruption, consider adding it with add_header. Also note that the Content-Length header is not set when using either version. Keepalives will therefore be impossible with version 1.0, while for 1.1 it is handled by chunked transfers.

- http://wiki.codemongers.com/NginxHttpGzipModule#gzip_http_version

Although it seems rather esoteric and isolated, this has big implications for people providing cloud hosted solutions trying to minimize bandwidth. Also, I see no compelling reason to continue using HTTP 1.0

I'm happy to write the 1 character patch it this will actually get committed. :)