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

[ooxi]

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.

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.