#2 getPublicKey function for x509 objects

[Andrey Lebedev]

I've made a patch for POW.c file that adds getPublicKey
function to x509 objects.

I use it as part of digital signature verification
routing using pem-encoded certificate file (to verify
signature you need to extract public key from
certificate first, then use that key to actually verify
the signature).

The patch also fixes compilation problem with recent
OpenSSLs.

[Andrey Lebedev]