Use sitename in forgotpassword email

htdocs/forgotpass.php

@@ -129,7 +129,7 @@ function forgotpass_submit($values) {
         $pwrequest->expiry = db_format_timestamp(time() + 86400);
         $pwrequest->key = get_random_key();
         email_user($user, null,
-            get_string('forgotpassemailsubject'),
+            get_string('forgotpassemailsubject', 'mahara', get_config('sitename')),
             get_string('forgotpassemailmessagetext', 'mahara', $pwrequest->key, $pwrequest->key),
             get_string('forgotpassemailmessagehtml', 'mahara', $pwrequest->key, $pwrequest->key, $pwrequest->key, $pwrequest->key));
         insert_record('usr_password_request', $pwrequest);

htdocs/lang/en.utf8/mahara.php

@@ -74,7 +74,7 @@ $string['registrationnosuchkey'] = 'Sorry, there does not seem to be a registrat
 
 // Forgot password
 $string['pwchangerequestsent'] = 'You should receive an e-mail shortly with a link you can use to change the password for your account';
-$string['forgotpassemailsubject'] = 'Change password request for Mahara';
+$string['forgotpassemailsubject'] = 'Change password request for %s';
 $string['forgotpassemailmessagetext'] = 'Dear $fullname,
 
 A request to reset your password has been received for your $sitename account.