Adding $opensslconfig to openssl_pkey_export()

In some situations openssl_pkey_export needs the configPath to openssl.cnf otherwise openssl is throwing strange errors - see attachment.
![Screen Shot 2013-03-01 at 14 51 24](https://f.cloud.github.com/assets/1678209/209674/38e74f94-8277-11e2-9c00-974564abfa2f.png)