Don't apply DNS name constraints to the subject CN when there's a
least one DNS-ID subjectAlternativeName.

Don't apply DNS name constraints to subject CN's that are sufficiently
unlike DNS names.  Checked name must have at least two labels, with
all labels non-empty, no trailing '.' and all hyphens must be
internal in each label.  In addition to the usual LDH characters,
we also allow "_", since some sites use these for hostnames despite
all the standards.
Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NTim Hudson <tjh@openssl.org>

subject alternate names.

Add nameConstraints tests incluing DNS, IP and email tests both in
subject alt name extension and subject name.
Reviewed-by: NRichard Levitte <levitte@openssl.org>