ISSUE 5261: Guest enroll message changed from error to info

Ticket link: http://atutor.ca/atutor/mantis/view.php?id=5261

I have made changes in enroll.php and atutor_language_text.sql. Now, on clicking 
"Enroll me", an info message of "You must be logged in to enroll in a course" is shown instead of the error message.