issues/456: basicAuth; do not show hint

[komuw]

• This was failing in mobile browsers. They were unable to show the username/password popup.
  I suspect that those clients only expect a header of the form www-authenticate: Basic realm=realmStr.
  Where realmStr is a string with no special characters. The docs say that realmStr is any string whose character set is us-ascii. The : colon symbol is part of us-ascii(number 58). So I don't know why it would cause mobile clients to fail.
• Fixes: basic auth error #456
• https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/WWW-Authenticate#realm