* helpful errors: print not only CN but also exactly what we are comparing
* helpful errors: return different errors for non-existent and unknown keys
* helpful errors: print error about encrypted key instead of "private key not found"
Break dataBundle into two pieces: inputBundle, which contains data that
is specific to the pki backend, and creationBundle, which is a more
generic bundle of validated inputs given to certificate creation/signing routines.
Move functions that only take creationBundle to certutil and make them public.
