Force using HTTP/1.1 since PayPal changed it's API

> In a bulletin dated October 18, 2011, we announced that we were going to expand the number of IP addresses for http://www.paypal.com to improve our site’s performance, scalability and availability. As part of this transition, we planned to discontinue support for HTTP 1.0 protocol starting October 7, 2013.
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> We have recently identified that this change may impact the ability of some of our merchants to perform IPN (Instant Payment Notification) post-back validation or PDT (Payment Data Transfer) posts to http://www.paypal.com and ipnpb.paypal.com. This happens when the IPN or PDT scripts use HTTP 1.0 protocol and do not include the “Host: http://www.paypal.com” or “Host: ipnpb.paypal.com” header in the HTTP request.