All of the payment processors make curl requests with CURLOPT_SSL_VERIFYPEER set to false

All CiviCRM payment processors set CURLOPT_SSL_VERIFYPEER to false when making curl requests to https servers. This is because curl ships with it's own list of CAs and it used to be a really bad list, so valid certificates would fail all the time. Now curl ships with a much better list of CAs, and it's safe to set CURLOPT_SSL_VERIFYPEER to true. I have tested all of the URLs that all of the payment processors make requests to, and they all pass except for https://www.sandbox.paypal.com/.

We should make verifying SSL certificates an option that defaults to yes in CiviCRM.

The attached php_curl_ssl.php is a script that makes curl requests to CiviCRM payment processor URLs with CURLOPT_SSL_VERIFYPEER set to true.