Email to a friend form needs required fields

Hi. As long as fileds in the email to a friend form are all required and skipping Message text returns validation error that this field must be filled in - I have added '#required' => TRUE, to this form and the patch agains v. 6.10 is attached.

Please review and port to the next module revision.

The advantages of having those additions are:
1. Forms API cares about validation (if fields left empty)
2. Usability improvement as user can see asterisk next to the required field