Fix memory leak in pkcs11_load_cert
The PKCS11_ resources can be free'd completely after looking up the cert as
the cert gets copied by X509_dup.
Numbers:
loading 100 certs:

before:
==15388== LEAK SUMMARY:
==15388==    definitely lost: 10,409 bytes in 112 blocks
==15388==    indirectly lost: 621,571 bytes in 14,009 blocks
==15388==      possibly lost: 35 bytes in 1 blocks
==15388==    still reachable: 1,684 bytes in 4 blocks
==15388==         suppressed: 0 bytes in 0 blocks

after:
==15585== LEAK SUMMARY:
==15585==    definitely lost: 2,409 bytes in 12 blocks
==15585==    indirectly lost: 406 bytes in 10 blocks
==15585==      possibly lost: 0 bytes in 0 blocks
==15585==    still reachable: 1,684 bytes in 4 blocks
==15585==         suppressed: 0 bytes in 0 blocks