The filemode code is enough different from the regular parser code that it

The filemode code is enough different from the regular parser code that it
makes sense to totally split it out. Duplicate proc_parser_cert_validate()
and proc_parser_root_cert() for now.

The valid_x509() plus the required static functions are moved to validate.c.
The crl_tree code moved into crl.c similar to the auth_tree handling in
cert.c. All the proc functions are now tagged with __attribute(noreturn)
which allows to remove the errx() after them.

OK tb@