Rework algorithmIdentifier parsing
pk_set_type() cannot be used to reset key type
Get rid of x509_cert.pkoid

Unused, comment did not match reality, and will soon be superseeded by the
'type' field of the pk_context which will replace rsa_context.
Factor more code into x509_get_pubkey()
Simplify length mismatch check in x509_get_pubkey
Rename x509_get_pubkey to _rsa and split it up
Introduce generic x509_get_pubkey()
Use new x509_get_pubkey() in x509parse_public_key()
Use generic x509_get_pubkey() for RSA functions
Expand oid_get_sig_alg() for ECDSA-based algs
Relax ifdef's in pk.h by analogy with md.h
Add test certificate signed with ECDSA
Fix warnings (enum value missing from switch/case)
Rename x509_get_algid() to x509_get_pk_alg()
Rationalize use of x509_get_alg variants
Prepare transition from x509_cert.rsa to pk
Adapt x509parse_cert_info() for EC
Fix bug in x509_get_{ecpubkey,subpubkey}()

- 'p' was not properly updated
- also add a few more checks while at it
Certificates with EC key and/or sig parsed
Adapt debug_print_crt() for EC keys