Adding hidden role assignment, currently used in course participants page and print_course function.

Please test.

admin/roles/assign.html

@@ -31,6 +31,8 @@
 
           </select></td>
       <td valign="top">
+        <input type="checkbox" name="hidden" value="1" />
+        <img src="<?php echo $CFG->pixpath; ?>/t/hide.gif" alt="<?php print_string('hiddenassign') ?>" class="hide-show-image" />
         <br />
         <input name="add" type="submit" id="add" value="&larr;" />
         <br />

admin/roles/assign.php

@@ -19,7 +19,7 @@
     $timeend        = optional_param('timened', 0, PARAM_INT);
     $userid         = optional_param('userid', 0, PARAM_INT); // needed for user tabs
     $courseid       = optional_param('courseid', 0, PARAM_INT); // needed for user tabs
-
+    
     $errors = array();
 
     $previoussearch = ($searchtext != '') or ($previoussearch) ? 1:0;