No proxy support using SQS

[jkoehl]

The async HTTP code is not allowing the proxy environment variables to be used by libcurl

It seems to be due to this code in async/http/curl.py

        if request.proxy_host:
            if not request.proxy_port:
                raise ValueError('Request with proxy_host but no proxy_port')
            setopt(_pycurl.PROXY, request.proxy_host)
            setopt(_pycurl.PROXYPORT, request.proxy_port)
            if request.proxy_username:
                setopt(_pycurl.PROXYUSERPWD, '{0}:{1}'.format(
                    request.proxy_username, request.proxy_password or ''))
        else:
            setopt(_pycurl.PROXY, '')
            curl.unsetopt(_pycurl.PROXYUSERPWD)

Notice that if the original request does not specify a proxy_host then it actually sets it to empty in the curl OPTs which makes libcurl NOT read the environment for it either.

And the caller in this case is the SQS transport which does NOT pass any proxy setting in either so when using SQS there doesn't appear to be a way to make Kombu use a proxy for the async HTTP.

(Note: The calls through Boto DO work because Boto reads it from the environment variables by default)