Deprecate the -issuer_checks debugging option

Deprecate the -issuer_checks debugging option

This was a developer debugging feature and was never a useful public
interface.

Added all missing X509 error codes to the verify(1) manpage, but
many still need a description beyond the associated text string.

Sorted the errors in x509_txt.c by error number.

Reviewed-by: Stephen Henson <steve@openssl.org>