now print out signatures instead of the standard hex dump.
More complex signatures (e.g. PSS) can print out more meaningful information.
Sample DSA version included that prints out the signature parameters r, s.
[Note EVP_PKEY_ASN1_METHOD is an application opaque structure so adding
new fields in the middle has no compatibility issues]
knock-on work than expected - they've been extracted into a patch
series that can be completed elsewhere, or in a different branch,
before merging back to HEAD.
