Invitation app removes hyphens in domain name and replaces them with strikethrough formatting

When using certain mail servers, it is necessary to use the Punycode representation of the domain name instead of the UTF-8 representation. For example, "foo@mañana.com" is technically "foo@xn--maana-pta.com" and needs to be written as such for non-Punycode-aware mail servers. However, XWiki removes the double hyphen and replaces it with strikethrough formatting, which is confusing. A similar problem occurs if the email address happens to contain a double underscore.

1. Go to http://localhost:8080/xwiki/bin/view/Invitation/
2. Send an invitation to foo@xn--maana-pta.com
3. Observe the result.
4. Click "My Invitations" and observe that this page has the problem too.

Screenshots of step 3 and step 4 are attached.