Disable HTTP 1.1 connection keep-alive

As [1] states:
If this value is set to 1.1 it is your responsibility to be 1.1
compliant.

PHP doesn't support Connection: keep-alive and feof will wait until the
timeout of the webserver it reached (5 seconds for Apache).

This patch adds Connection: close to the headers of PHPStreamTransport
to prevent keep-alive for HTTP 1.1 requests.

1. http://www.php.net/manual/en/context.http.php#context.http.protocol-version