Verifies a dNSName for HTTPS usage, (almost) as per Firefox's rules:
- Wildcards can only occur in a name with more than 3 components
- Wildcards can only occur as the last character in the first component
- Wildcards may be preceded by additional characters
We modify these rules to be a bit stricter and only allow the wildcard
character to be the full first component; that is, with the exclusion of
the third rule.