Remove SSL version 3 support.

This commit mirrors Hopu-Ka-Lewa-website commit de82f186ceaf003df3460aa88cae18f361447686.

Per the original IPN listener author's repo pull request 32: [Quixotix/PHP-PayPal-IPN#32](https://github.com/Quixotix/PHP-PayPal-IPN/pull/32).
(This pull request had not yet been pulled into the original repo at the time of this edit.)

PayPal has stopped supporting SSLv3, so we have to as well.