Fix for bug66501 - key type not supported in this PHP build

Solving "key type not supported in this PHP build" error for bug 66501:
https://bugs.php.net/bug.php?id=66501
by adding EC support to php_openssl_is_private_key

also includes unit test that expects
PHP Warning: openssl_sign(): key type not supported in this PHP build!
not to be emitted